Actually I have 2 questions:
1. How do I add include directories to the g++ call? I have tried using the visual studio directories (Which seems to update intellisense, but not the build), and I have tried adding via -I pointing to my copied directory, for example:
-I"External\StandardCplusplus"

That shows up in the build, but doesnt seem to work, as you can see here:

\4.8.3-2014q1\bin\arm-none-eabi-g++" -c -g -Os -w -std=gnu++11 -ffunction-sections -fdata-sections -nostdlib -fno-threadsafe-statics --param max-inline-insns-single=500 -fno-rtti -fno-exceptions -DVM_DEBUG_BREAKPAUSE -DVM_DEBUGGER_TYPE=VM_DEBUGGER_TYPE_UART -DVM_DEBUGGER_TYPE_SERIALUSB=18 -DVM_DEBUGGER_TYPE_USBAPI=17 -DVM_DEBUGGER_TYPE_NET_UDP=16 -DVM_DEBUGGER_TYPE_HARDWARESERIAL3=15 -DVM_DEBUGGER_TYPE_HARDWARESERIAL2=14 -DVM_DEBUGGER_TYPE_HARDWARESERIAL1=13 -DVM_DEBUGGER_TYPE_CDCSerialClass=12 -DVM_DEBUGGER_TYPE_COSA=11 -DVM_DEBUGGER_TYPE_Uart=10 -DVM_DEBUGGER_TYPE_NET_CONSOLE=9 -DVM_DEBUGGER_TYPE_TTYUART=8 -DVM_DEBUGGER_TYPE_USBSERIAL=7 -DVM_DEBUGGER_TYPE_USART=6 -DVM_DEBUGGER_TYPE_UART=5 -DVM_DEBUGGER_TYPE_TEENSY=4 -DVM_DEBUGGER_TYPE_USB=3 -DVM_DEBUGGER_TYPE_FASTSERIAL=2 -DVM_DEBUGGER_TYPE_SOFTWARESERIAL=1 -DVM_DEBUGGER_TYPE_HARDWARESERIAL=0 -DVM_DEBUG_BANDWIDTH_THROTTLE_MS=100 -DVM_DEBUG_ENABLE=1 -DVM_DEBUG  -fpermissive -I"External\StandardCplusplus"   -Dprintf=iprintf -w -x c++ -E -CC -mcpu=cortex-m3 -mthumb -DF_CPU=84000000L -DARDUINO=10804 -DARDUINO_SAM_DUE -DARDUINO_ARCH_SAM -D__SAM3X8E__ -mthumb -DUSB_VID=0x2341 -DUSB_PID=0x003e -DUSBCON -DUSB_MANUFACTURER="\"Arduino LLC\"" -DUSB_PRODUCT="\"Arduino Due\"" ystem/libsam" ystem/CMSIS/CMSIS/Include/" ystem/CMSIS/Device/ATMEL/" ores\arduino" ariants\arduino_due_x" ibraries\SPI\src" -I"C:\Program Files (x86)\Microsoft Visual Studio\2017\Community\Common7\IDE\Extensions\53ggn0bh.0i3\Micro Platforms\default\debuggers\VM_DBG" \External\StandardCplusplus\associative_base.cpp" -o "nul"

associative_base.cpp: 20:28: fatal error: associative_base: No such file or directory
   #include "associative_base"
   compilation terminated
Debug build failed for project 'uWindowsTest'
 

Is it possible to ${} the build dir in an include?
2nd question or request.  It would be nice if we could set includes in shared library projects, that got propagated up to the project that uses them.

THANKS!
Ron

Ok, so how would I include a directory?

Sigh, we arent communicating well.

What I want to do is include a directory (I misspoke when I said library).

So, if I included said code as an Arduino style library the includes would be taken care of.

What I have is a Shared Library and a necessary include inside of it.

For example:
SharedLibrary/External/LIB

I want to include LIB in my build, the issue is when I do -I"SharedLibrary/External/LIB" it doesnt propagate out correctly.  When it is building code in the shared library, as opposed to the project that includes it, I get include not found errors (Which I dont in the base project).

So, obviously -I wont work with the relative directory, is there a way to push the -I down to the shared library?

Okay so lets forget the word library?

You can add a compiler -I in the Visual Micro project properties flags or includes property. However this often causes confusion because all you get is a compiler include. The compiler will not look at the include and compile the code in the included folder. So if all you need are references in a .h then it might be okay.

However you could make the external code a Visual Studio shared project and then add a Reference to the arduino project. Visual Micro will detect this and copy the external code into the temp directory tree used for compile. In that case the following might work for you.

I am unclear from your post the actual structure of your external code. I will assume that some files exist in the folder called "SharedLibrary" therefore SharedLibrary will be where our shared project is created

ArduinoProject1
   ArduinoProject1.ino
   ArduinoCpp.cpp

SharedLibrary
   some.cpp
   SharedLibrary/External/LIB
      someheader.h

In this case the files in SharedLibrary will be located in the same folder as ArduinoProject1.ino during compile.  Our ArduinoProject1.ino code can reference files from \LIB with a relative path #include "External/LIB/someheader.h"

A compiler include of -I"{project_folder}/External/LIB" might also work

What I am looking for is the variable that represents the bold here in the command line:

\4.8.3-2014q1\bin\arm-none-eabi-g++" -c -g -Os -w -std=gnu++11 -ffunction-sections -fdata-sections -nostdlib -fno-threadsafe-statics --param max-inline-insns-single=500 -fno-rtti -fno-exceptions -DVM_DEBUG_BREAKPAUSE -DVM_DEBUGGER_TYPE=VM_DEBUGGER_TYPE_UART -DVM_DEBUGGER_TYPE_SERIALUSB=18 -DVM_DEBUGGER_TYPE_USBAPI=17 -DVM_DEBUGGER_TYPE_NET_UDP=16 -DVM_DEBUGGER_TYPE_HARDWARESERIAL3=15 -DVM_DEBUGGER_TYPE_HARDWARESERIAL2=14 -DVM_DEBUGGER_TYPE_HARDWARESERIAL1=13 -DVM_DEBUGGER_TYPE_CDCSerialClass=12 -DVM_DEBUGGER_TYPE_COSA=11 -DVM_DEBUGGER_TYPE_Uart=10 -DVM_DEBUGGER_TYPE_NET_CONSOLE=9 -DVM_DEBUGGER_TYPE_TTYUART=8 -DVM_DEBUGGER_TYPE_USBSERIAL=7 -DVM_DEBUGGER_TYPE_USART=6 -DVM_DEBUGGER_TYPE_UART=5 -DVM_DEBUGGER_TYPE_TEENSY=4 -DVM_DEBUGGER_TYPE_USB=3 -DVM_DEBUGGER_TYPE_FASTSERIAL=2 -DVM_DEBUGGER_TYPE_SOFTWARESERIAL=1 -DVM_DEBUGGER_TYPE_HARDWARESERIAL=0 -DVM_DEBUG_BANDWIDTH_THROTTLE_MS=100 -DVM_DEBUG_ENABLE=1 -DVM_DEBUG  -fpermissive -I"/External/StandardCplusplus"   -Dprintf=iprintf -w -x c++ -E -CC -mcpu=cortex-m3 -mthumb -DF_CPU=84000000L -DARDUINO=10804 -DARDUINO_SAM_DUE -DARDUINO_ARCH_SAM -D__SAM3X8E__ -mthumb -DUSB_VID=0x2341 -DUSB_PID=0x003e -DUSBCON -DUSB_MANUFACTURER="\"Arduino LLC\"" -DUSB_PRODUCT="\"Arduino Due\"" ystem/libsam" ystem/CMSIS/CMSIS/Include/" ystem/CMSIS/Device/ATMEL/" ores\arduino" ariants\arduino_due_x" ibraries\SPI\src" -I"C:\Program Files (x86)\Microsoft Visual Studio\2017\Community\Common7\IDE\Extensions\53ggn0bh.0i3\Micro Platforms\default\debuggers\VM_DBG" \External\StandardCplusplus\associative_base.cpp" -o "nul"

Ah. Okay I will copy them over but ignore them during compile. Try to make a release over the next few days

Honestly Ive never written a VS plugin (Gave it some thought when I worked at Microsoft, then just asked the DevDiv guys for the ask).

But this is how I would expect the flow to be on my end:
Simple work flow:
1. If it is included in the project, copy it
2. If it is included and a cpp/c compile it

I am sure I left out 1000 nuances, but you get the idea.