build: reset LLVM warning flags

LLVM unfortunately defines global compile flags that are inherited by all other targets in the project, including fetched dependencies. Warning flags, with are functionally unnecessary, can cause conflicts with other targets.

fix cppalliance#251

Author: alandefreitas

CMakeLists.txt

@@ -77,11 +77,25 @@ endif()
 
 set(CMAKE_FOLDER Dependencies)
 
+macro(add_variable_override var_name var_val)
+    macro(handle_${var_name}_access var)
+        set(${var} ${var_val})
+    endmacro()
+    variable_watch(${var_name} handle_${var_name}_access)
+endmacro()
+
+macro(remove_variable_override var_name)
+    macro(handle_${var_name}_access)
+    endmacro()
+endmacro()
+
 # LLVM
 find_package(LLVM REQUIRED CONFIG)
 find_package(Clang REQUIRED CONFIG)
 list(APPEND CMAKE_MODULE_PATH "${LLVM_CMAKE_DIR}")
+add_variable_override(msvc_warning_flags "")
 include(HandleLLVMOptions)
+remove_variable_override(msvc_warning_flags)
 add_definitions(${LLVM_DEFINITIONS})
 llvm_map_components_to_libnames(llvm_libs all)
 
@@ -181,16 +195,24 @@ if (WIN32)
     get_target_property(LLVM_CONFIGURATION_TYPE LLVMCore IMPORTED_CONFIGURATIONS)
     if (LLVM_CONFIGURATION_TYPE STREQUAL RELWITHDEBINFO)
         target_compile_definitions(mrdox PUBLIC -D_ITERATOR_DEBUG_LEVEL=0)
-        target_compile_options(mrdox PUBLIC /MD)
+        # target_compile_options(mrdox PUBLIC /MD)
     endif()
     if(MSVC)
         target_compile_options(
             mrdox
             PUBLIC
             /permissive-    # strict C++
-            /W4             # enable all warnings
             /MP             # multi-processor compilation
             /EHsc           # C++ Exception handling
+            /W4             # enable all warnings
+            /wd4100         # unreferenced formal parameter
+            /wd4702         # unreachable code
+            /wd4706         # assignment within conditional expression
+            /wd4244         # narrowing integral conversion
+            /wd4267         # narrowing std::size_t conversion
+            /wd4456         # declaration hides local declaration
+            /wd4457         # declaration hides function parameter declaration
+            /wd4459         # declaration hides global declaration
         )
     endif()
 endif ()