Add explicit symbol exports for Flashlight core (flashlight#1141)

Summary:
Remove the need to export all symbols for MSVC-based builds, and explicitly export symbols throughout the Flashlight API. This removes the need to use `CMAKE_WINDOWS_EXPORT_ALL_SYMBOLS` and makes Windows build sizes significantly smaller.

Subsequent exports for `pkg` and `app` will be added separately; this isn't being prioritized

Pull Request resolved: flashlight#1141

Test Plan:
local build + CI

----
:books: Documentation preview :books:: https://fl--1141.org.readthedocs.build/en/1141/

Reviewed By: bwasti

Differential Revision: D50092087

Pulled By: jacobkahn

fbshipit-source-id: 5b4f3aed8866353dc7c49172817b4e3e9e2321ff

.circleci/config.yml

@@ -401,8 +401,7 @@ commands:
               -DFL_USE_ONEDNN=$([ "<< parameters.backend >>" == "onednn" ] || [ "<< parameters.autograd_backend >>" == "onednn" ] && echo "ON" || echo "OFF") \
               -DFL_USE_NCCL=$(([ "<< parameters.platform >>" == "linux" ] || [ "<< parameters.platform >>" == "windows" ]) && [ "<< parameters.distributed_backend >>" == "nccl" ] && echo "ON" || echo "OFF") \
               -DFL_USE_GLOO=OFF \
-              -DFL_USE_BACKWARD_CPP=ON \
-              -DCMAKE_WINDOWS_EXPORT_ALL_SYMBOLS=ON
+              -DFL_USE_BACKWARD_CPP=ON
             cmake --build build --parallel << parameters.build_parallelism >>
 
   test-flashlight:

.github/workflows/build.yml

@@ -49,8 +49,7 @@ jobs:
             -DFL_USE_TENSOR_STUB=${{ matrix.backend == 'Stub' && 'ON' || 'OFF'  }} \
             -DFL_USE_NCCL=OFF \
             -DFL_USE_GLOO=${{ matrix.distributed_backend == 'Gloo' && 'ON' || 'OFF'  }} \
-            -DFL_USE_BACKWARD_CPP=ON \
-            -DCMAKE_WINDOWS_EXPORT_ALL_SYMBOLS=ON
+            -DFL_USE_BACKWARD_CPP=ON
       - name: "Build Flashlight"
         run: |
           cmake --build build --parallel 2

CMakeLists.txt

@@ -114,6 +114,9 @@ target_compile_definitions(flashlight
   FL_BACKEND_CPU=$<BOOL:${FL_USE_CPU}>
   FL_BACKEND_CUDA=$<BOOL:${FL_USE_CUDA}>
   FL_BUILD_PROFILING=$<BOOL:${FL_BUILD_PROFILING}>
+  FL_COMPILE_LIBRARY=$<BOOL:${BUILD_SHARED_LIBS}>
+  PRIVATE
+  FL_DLL
   )
 
 if (FL_CODE_COVERAGE)

flashlight/app/CMakeLists.txt

@@ -22,6 +22,10 @@ function(register_app)
   )
 
   if(${_option_name})
+    if (MSVC)
+      message(FATAL_ERROR "Building fl packages (pkg) with MSVC not yet supported")
+    endif()
+
     message(STATUS "Building Flashlight ${_app_name_lower} package.")
     include(${FL_APPS_DIR}/${_app_name_lower}/CMakeLists.txt)
   endif()