cmake: Add TryAppendCXXFlags module

cmake/module/TryAppendCXXFlags.cmake

@@ -0,0 +1,85 @@
+# Copyright (c) 2023-present The Bitcoin Core developers
+# Distributed under the MIT software license, see the accompanying
+# file COPYING or https://opensource.org/license/mit/.
+
+include_guard(GLOBAL)
+include(CheckCXXSourceCompiles)
+
+#[=[
+Usage examples:
+
+  try_append_cxx_flags(warn_cxx_flags "-Wformat -Wformat-security")
+
+
+  try_append_cxx_flags(warn_cxx_flags "-Wsuggest-override"
+    SOURCE "struct A { virtual void f(); }; struct B : A { void f() final; };"
+  )
+
+
+  try_append_cxx_flags(sanitizers_cxx_flags "-fsanitize=${SANITIZERS}" RESULT_VAR cxx_supports_sanitizers)
+  if(NOT cxx_supports_sanitizers)
+    message(FATAL_ERROR "Compiler did not accept requested flags.")
+  endif()
+
+
+  try_append_cxx_flags(warn_cxx_flags "-Wunused-parameter" IF_CHECK_PASSED "-Wno-unused-parameter")
+
+
+  try_append_cxx_flags(error_cxx_flags "-Werror=return-type"
+    IF_CHECK_FAILED "-Wno-error=return-type"
+    SOURCE "#include <cassert>\nint f(){ assert(false); }"
+  )
+
+
+In configuration output, this function prints a string by the following pattern:
+
+  -- Performing Test CXX_SUPPORTS_[flags]
+  -- Performing Test CXX_SUPPORTS_[flags] - Success
+
+]=]
+function(try_append_cxx_flags flags_var flags)
+  cmake_parse_arguments(PARSE_ARGV 2
+    TACXXF                            # prefix
+    ""                                # options
+    "SOURCE;RESULT_VAR"               # one_value_keywords
+    "IF_CHECK_PASSED;IF_CHECK_FAILED" # multi_value_keywords
+  )
+
+  string(MAKE_C_IDENTIFIER "${flags}" result)
+  string(TOUPPER "${result}" result)
+  set(result "CXX_SUPPORTS_${result}")
+
+  # Every subsequent check_cxx_source_compiles((<code> <resultVar>) run will re-use
+  # the cached result rather than performing the check again, even if the <code> changes.
+  # Removing the cached result in order to force the check to be re-evaluated.
+  unset(${result} CACHE)
+
+  if(NOT DEFINED TACXXF_SOURCE)
+    set(TACXXF_SOURCE "int main() { return 0; }")
+  endif()
+
+  # This avoids running a linker.
+  set(CMAKE_TRY_COMPILE_TARGET_TYPE STATIC_LIBRARY)
+  set(CMAKE_REQUIRED_FLAGS "${flags} ${working_compiler_werror_flag}")
+  check_cxx_source_compiles("${TACXXF_SOURCE}" ${result})
+
+  if(${result})
+    if(DEFINED TACXXF_IF_CHECK_PASSED)
+      string(STRIP "${${flags_var}} ${TACXXF_IF_CHECK_PASSED}" ${flags_var})
+    else()
+      string(STRIP "${${flags_var}} ${flags}" ${flags_var})
+    endif()
+  elseif(DEFINED TACXXF_IF_CHECK_FAILED)
+    string(STRIP "${${flags_var}} ${TACXXF_IF_CHECK_FAILED}" ${flags_var})
+  endif()
+  set(${flags_var} "${${flags_var}}" PARENT_SCOPE)
+  set(${TACXXF_RESULT_VAR} "${${result}}" PARENT_SCOPE)
+endfunction()
+
+if(MSVC)
+  set(warning_as_error_flag /WX)
+else()
+  set(warning_as_error_flag -Werror)
+endif()
+try_append_cxx_flags(working_compiler_werror_flag ${warning_as_error_flag})
+unset(warning_as_error_flag)