Paramatized rust_static_library to enable CXX support

Summary:
X-link: facebookincubator/delos_core#8

X-link: facebookincubator/zstrong#610

X-link: facebookincubator/crux#10

X-link: facebookexternal/traffixr#3

X-link: facebookincubator/katran#205

X-link: facebookincubator/fizz#101

X-link: facebook/sapling#763

X-link: facebookexperimental/rust-shed#43

X-link: facebook/wangle#221

X-link: facebook/openr#150

X-link: facebook/hhvm#9403

X-link: facebook/folly#2092

X-link: facebook/fb303#42

X-link: facebookincubator/velox#7301

We are now using CXX (and not just bindgen/cbindgen) for building our Rust C/C++ APIS, but our OSS tooling did not ergomically support this. This change adds a single option, `USE_CXX_INCLUDE`, to the CMake function, `rust_static_library`, to enable adding the `cxxbridge` path to the include path.

Reviewed By: xavierd

Differential Revision: D50772544

build/fbcode_builder/CMake/RustStaticLibrary.cmake

@@ -80,7 +80,7 @@ set_property(GLOBAL APPEND PROPERTY JOB_POOLS rust_job_pool=1)
 # Cargo build static library.
 #
 # ```cmake
-# rust_static_library(<TARGET> [CRATE <CRATE_NAME>] [FEATURES <FEATURE_NAME>])
+# rust_static_library(<TARGET> [CRATE <CRATE_NAME>] [FEATURES <FEATURE_NAME>] [USE_CXX_INCLUDE])
 # ```
 #
 # Parameters:
@@ -92,6 +92,8 @@ set_property(GLOBAL APPEND PROPERTY JOB_POOLS rust_job_pool=1)
 #   fallback to `${TARGET}`.
 # - FEATURE_NAME:
 #   Name of the Rust feature to enable.
+# - USE_CXX_INCLUDE:
+#   Include cxx.rs include path in `${TARGET}` INTERFACE.
 #
 # This function creates two targets:
 # - "${TARGET}": an interface library target contains the static library built
@@ -103,7 +105,7 @@ set_property(GLOBAL APPEND PROPERTY JOB_POOLS rust_job_pool=1)
 # headers with the interface library.
 #
 function(rust_static_library TARGET)
-  fb_cmake_parse_args(ARG "" "CRATE;FEATURES" "" "${ARGN}")
+  fb_cmake_parse_args(ARG "USE_CXX_INCLUDE" "CRATE;FEATURES" "" "${ARGN}")
 
   if(DEFINED ARG_CRATE)
     set(crate_name "${ARG_CRATE}")
@@ -158,6 +160,14 @@ function(rust_static_library TARGET)
       INTERFACE_INSTALL_LIBNAME
         "${CMAKE_STATIC_LIBRARY_PREFIX}${crate_name}_rs${CMAKE_STATIC_LIBRARY_SUFFIX}"
   )
+
+  if(DEFINED ARG_USE_CXX_INCLUDE)
+    target_include_directories(
+      ${TARGET}
+      INTERFACE ${CMAKE_CURRENT_BINARY_DIR}/cxxbridge/
+    )
+  endif()
+
   target_link_libraries(
     ${TARGET}
     INTERFACE "$<BUILD_INTERFACE:${rust_staticlib}>"