Small Warnings Refactor (#4477)

* Disable all warnings, even in release, on the `src` directory.
Resolve math macro duplication warnings.

* Suppress LUS warnings.

* Modify it to utilize a variable that defaults on but can be specified in command line to disable it.
Prevet total compile option overwrite for LUS.

* Remove unnecessary unset and cache parameters.

* Document warnings flag in BUILDING.md

soh/CMakeLists.txt

@@ -173,6 +173,7 @@ endif()
 
 # src (decomp) {{{
 file(GLOB_RECURSE src__ RELATIVE ${CMAKE_CURRENT_SOURCE_DIR} "src/*.c" "src/*.h")
+set_source_files_properties(${src__} PROPERTIES COMPILE_OPTIONS "${WARNING_OVERRIDE}")
 
 list(APPEND src__ ${CMAKE_CURRENT_SOURCE_DIR}/Resource.rc)
 list(FILTER src__ EXCLUDE REGEX "src/dmadata/*")