[cmake] Centralize LLVM_ENABLE_WARNINGS option

Configure default value of `LLVM_ENABLE_WARNINGS` in `HandleLLVMOptions.cmake`.

`LLVM_ENABLE_WARNINGS` is documented as ON by default, but `HandleLLVMOptions` assumes the default has been set somewhere else. If it has not been explicitly set, then `HandleLLVMOptions` implicitly uses OFF as a default.

This removes the various `option()` declarations in favor of a single declaration in `HandleLLVMOptions`. This will prevent the unwanted use of `-w` that is mentioned in a couple of the comments.

Reviewed By: DavidTruby, #libunwind, JDevlieghere, compnerd

Differential Revision: https://reviews.llvm.org/D87243

(cherry picked from commit b36bdfe)

Author: kastiglione

clang/CMakeLists.txt

@@ -105,7 +105,6 @@ if( CMAKE_SOURCE_DIR STREQUAL CMAKE_CURRENT_SOURCE_DIR )
     set(LLVM_SHLIB_OUTPUT_INTDIR ${LLVM_LIBRARY_OUTPUT_INTDIR})
   endif()
 
-  option(LLVM_ENABLE_WARNINGS "Enable compiler warnings." ON)
   option(LLVM_INSTALL_TOOLCHAIN_ONLY
     "Only include toolchain files in the 'install' target." OFF)
 

flang/CMakeLists.txt

@@ -62,7 +62,6 @@ if (CMAKE_SOURCE_DIR STREQUAL CMAKE_CURRENT_SOURCE_DIR)
   if(LLVM_ENABLE_ZLIB)
     find_package(ZLIB REQUIRED)
   endif()
-  option(LLVM_ENABLE_WARNINGS "Enable compiler warnings." ON)
   option(LLVM_ENABLE_PEDANTIC "Compile with pedantic enabled." ON)
 
   include(CMakeParseArguments)

libunwind/CMakeLists.txt

@@ -73,8 +73,6 @@ if (CMAKE_SOURCE_DIR STREQUAL CMAKE_CURRENT_SOURCE_DIR OR LIBUNWIND_STANDALONE_B
   endif()
 
   if (EXISTS ${LLVM_CMAKE_PATH})
-    # Enable warnings, otherwise -w gets added to the cflags by HandleLLVMOptions.
-    set(LLVM_ENABLE_WARNINGS ON)
     list(APPEND CMAKE_MODULE_PATH "${LLVM_CMAKE_PATH}")
     include("${LLVM_CMAKE_PATH}/AddLLVM.cmake")
     include("${LLVM_CMAKE_PATH}/HandleLLVMOptions.cmake")

llvm/CMakeLists.txt

@@ -402,7 +402,6 @@ set(LLVM_TARGETS_TO_BUILD
 list(REMOVE_DUPLICATES LLVM_TARGETS_TO_BUILD)
 
 option(LLVM_ENABLE_PIC "Build Position-Independent Code" ON)
-option(LLVM_ENABLE_WARNINGS "Enable compiler warnings." ON)
 option(LLVM_ENABLE_MODULES "Compile with C++ modules enabled." OFF)
 if(${CMAKE_SYSTEM_NAME} MATCHES "Darwin")
   option(LLVM_ENABLE_MODULE_DEBUGGING "Compile with -gmodules." ON)

llvm/cmake/modules/HandleLLVMOptions.cmake

@@ -400,6 +400,8 @@ elseif(MINGW) # FIXME: Also cygwin?
   endif()
 endif()
 
+option(LLVM_ENABLE_WARNINGS "Enable compiler warnings." ON)
+
 if( MSVC )
   include(ChooseMSVCCRT)
 

llvm/cmake/modules/LLVMConfig.cmake.in

@@ -38,6 +38,8 @@ set(TARGET_TRIPLE "@TARGET_TRIPLE@")
 
 set(LLVM_ABI_BREAKING_CHECKS @LLVM_ABI_BREAKING_CHECKS@)
 
+set(LLVM_ENABLE_WARNINGS @LLVM_ENABLE_WARNINGS@)
+
 set(LLVM_ENABLE_EXPENSIVE_CHECKS @LLVM_ENABLE_EXPENSIVE_CHECKS@)
 
 set(LLVM_ENABLE_ASSERTIONS @LLVM_ENABLE_ASSERTIONS@)

llvm/runtimes/CMakeLists.txt

@@ -105,10 +105,6 @@ if(${CMAKE_SOURCE_DIR} STREQUAL ${CMAKE_CURRENT_SOURCE_DIR})
   # Avoid checking whether the compiler is working.
   set(LLVM_COMPILER_CHECKED ON)
 
-  # Enable warnings, otherwise -w gets added to the cflags by HandleLLVMOptions
-  # resulting in unjustified successes by check_cxx_compiler_flag.
-  set(LLVM_ENABLE_WARNINGS ON)
-
   # Handle common options used by all runtimes.
   include(AddLLVM)
   include(HandleLLVMOptions)