libclang: Make shared object symbol exporting by default

https://reviews.llvm.org/D74564 enabled static building for libclang,
and for non CMake consumers they had to set the `CMAKE_EXPORTS` define
when consuming libclang.

This commit makes the non CMake users of the static building have to define `CMAKE_NO_EXPORTS`.

Differential Revision: https://reviews.llvm.org/D74907

clang/include/clang-c/Platform.h

@@ -19,6 +19,9 @@
 LLVM_CLANG_C_EXTERN_C_BEGIN
 
 /* Windows DLL import/export. */
+#ifndef CINDEX_NO_EXPORTS
+  #define CINDEX_EXPORTS
+#endif
 #ifdef _WIN32
   #ifdef CINDEX_EXPORTS
     #ifdef _CINDEX_LIB_
@@ -27,7 +30,7 @@ LLVM_CLANG_C_EXTERN_C_BEGIN
       #define CINDEX_LINKAGE __declspec(dllimport)
     #endif
   #endif
-#elif defined(CINDEX_EXPORTS)
+#elif defined(CINDEX_EXPORTS) && defined(__GNUC__)
   #define CINDEX_LINKAGE __attribute__((visibility("default")))
 #endif
 

clang/tools/libclang/CMakeLists.txt

@@ -77,7 +77,7 @@ if(MSVC)
   set(LLVM_EXPORTED_SYMBOL_FILE)
 endif()
 
-if(LLVM_ENABLE_PIC)
+if(LLVM_ENABLE_PIC OR NOT LIBCLANG_BUILD_STATIC)
   set(ENABLE_SHARED SHARED)
 endif()
 
@@ -113,8 +113,15 @@ add_clang_library(libclang ${ENABLE_SHARED} ${ENABLE_STATIC} INSTALL_WITH_TOOLCH
   Support
   )
 
+if(ENABLE_STATIC)
+  foreach(name libclang obj.libclang libclang_static)
+    if (TARGET ${name})
+      target_compile_definitions(${name} PUBLIC CINDEX_NO_EXPORTS)
+    endif()
+  endforeach()
+endif()
+
 if(ENABLE_SHARED)
-  target_compile_definitions(libclang PUBLIC CINDEX_EXPORTS)
   if(WIN32)
     set_target_properties(libclang
       PROPERTIES