PCH: Mark CMake PCH source files as -x <lang>-header

Fixes: #21163

Modules/CMakeOBJCXXInformation.cmake

@@ -263,7 +263,7 @@ endif()
 # compile an Objective-C++ file into an object file
 if(NOT CMAKE_OBJCXX_COMPILE_OBJECT)
   set(CMAKE_OBJCXX_COMPILE_OBJECT
-    "<CMAKE_OBJCXX_COMPILER> <DEFINES> <INCLUDES> <FLAGS> -x objective-c++ -o <OBJECT> -c <SOURCE>")
+    "<CMAKE_OBJCXX_COMPILER> <DEFINES> <INCLUDES> <FLAGS> -o <OBJECT> -c <SOURCE>")
 endif()
 
 if(NOT CMAKE_OBJCXX_LINK_EXECUTABLE)

Modules/Compiler/Clang.cmake

@@ -10,6 +10,11 @@ set(__COMPILER_CLANG 1)
 
 include(Compiler/CMakeCommonCompilerMacros)
 
+set(__pch_header_C "c-header")
+set(__pch_header_CXX "c++-header")
+set(__pch_header_OBJC "objective-c-header")
+set(__pch_header_OBJCXX "objective-c++-header")
+
 if("x${CMAKE_C_SIMULATE_ID}" STREQUAL "xMSVC"
     OR "x${CMAKE_CXX_SIMULATE_ID}" STREQUAL "xMSVC"
     OR "x${CMAKE_Fortran_SIMULATE_ID}" STREQUAL "xMSVC")
@@ -102,7 +107,7 @@ else()
       set(CMAKE_PCH_PROLOGUE "#pragma clang system_header")
     endif()
     set(CMAKE_${lang}_COMPILE_OPTIONS_USE_PCH -Xclang -include-pch -Xclang <PCH_FILE> -Xclang -include -Xclang <PCH_HEADER>)
-    set(CMAKE_${lang}_COMPILE_OPTIONS_CREATE_PCH -Xclang -emit-pch -Xclang -include -Xclang <PCH_HEADER>)
+    set(CMAKE_${lang}_COMPILE_OPTIONS_CREATE_PCH -Xclang -emit-pch -Xclang -include -Xclang <PCH_HEADER> -x ${__pch_header_${lang}})
   endmacro()
 endif()
 

Modules/Platform/Windows-Clang.cmake

@@ -8,6 +8,11 @@ if(__WINDOWS_CLANG)
 endif()
 set(__WINDOWS_CLANG 1)
 
+set(__pch_header_C "c-header")
+set(__pch_header_CXX "c++-header")
+set(__pch_header_OBJC "objective-c-header")
+set(__pch_header_OBJCXX "objective-c++-header")
+
 macro(__windows_compiler_clang_gnu lang)
   set(CMAKE_LIBRARY_PATH_FLAG "-L")
   set(CMAKE_LINK_LIBRARY_FLAG "-l")
@@ -87,7 +92,7 @@ macro(__windows_compiler_clang_gnu lang)
   set(CMAKE_PCH_EXTENSION .pch)
   set(CMAKE_PCH_PROLOGUE "#pragma clang system_header")
   set(CMAKE_${lang}_COMPILE_OPTIONS_USE_PCH -Xclang -include-pch -Xclang <PCH_FILE> -Xclang -include -Xclang <PCH_HEADER>)
-  set(CMAKE_${lang}_COMPILE_OPTIONS_CREATE_PCH -Xclang -emit-pch -Xclang -include -Xclang <PCH_HEADER>)
+  set(CMAKE_${lang}_COMPILE_OPTIONS_CREATE_PCH -Xclang -emit-pch -Xclang -include -Xclang <PCH_HEADER> -x ${__pch_header_${lang}})
 
   unset(__ADDED_FLAGS)
   unset(__ADDED_FLAGS_DEBUG)

Modules/Platform/Windows-Embarcadero.cmake

@@ -10,6 +10,11 @@ set(__WINDOWS_EMBARCADERO 1)
 
 set(BORLAND 1)
 
+set(__pch_header_C "c-header")
+set(__pch_header_CXX "c++-header")
+set(__pch_header_OBJC "objective-c-header")
+set(__pch_header_OBJCXX "objective-c++-header")
+
 if("${CMAKE_${_lang}_COMPILER_VERSION}" VERSION_LESS 6.30)
   # Borland target type flags (bcc32 -h -t):
   set(_tW "-tW")       # -tW  GUI App         (implies -U__CONSOLE__)
@@ -123,7 +128,7 @@ macro(__embarcadero_language lang)
   if (EMBARCADERO)
     set(CMAKE_PCH_EXTENSION .pch)
     set(CMAKE_${lang}_COMPILE_OPTIONS_USE_PCH -Xclang -include-pch -Xclang <PCH_FILE> -Xclang -include -Xclang <PCH_HEADER>)
-    set(CMAKE_${lang}_COMPILE_OPTIONS_CREATE_PCH -Xclang -emit-pch -Xclang -include -Xclang <PCH_HEADER>)
+    set(CMAKE_${lang}_COMPILE_OPTIONS_CREATE_PCH -Xclang -emit-pch -Xclang -include -Xclang <PCH_HEADER> -x ${__pch_header_${lang}})
   endif()
 
   # Initial configuration flags.