warnings: Treat warnings as error

This way warnings will be taken seriously, and will cause PR checks to
fail when they throw warnings.

Author: Riksu9000

src/CMakeLists.txt

@@ -772,7 +772,7 @@ link_directories(
 
 
 set(COMMON_FLAGS -MP -MD -mthumb -mabi=aapcs -ftree-vrp -ffunction-sections -fdata-sections -fno-strict-aliasing -fno-builtin -fshort-enums -mcpu=cortex-m4 -mfloat-abi=hard -mfpu=fpv4-sp-d16 -fstack-usage -fno-exceptions -fno-non-call-exceptions)
-set(WARNING_FLAGS -Wall -Wextra -Warray-bounds=2 -Wformat=2 -Wformat-overflow=2 -Wformat-truncation=2 -Wformat-nonliteral -Wno-missing-field-initializers -Wno-unknown-pragmas -Wno-expansion-to-defined -Wreturn-type -Werror=return-type)
+set(WARNING_FLAGS -Wall -Wextra -Warray-bounds=2 -Wformat=2 -Wformat-overflow=2 -Wformat-truncation=2 -Wformat-nonliteral -Wno-missing-field-initializers -Wno-unknown-pragmas -Wno-expansion-to-defined -Wreturn-type -Werror=return-type -Werror)
 set(DEBUG_FLAGS -Og -g3)
 set(RELEASE_FLAGS -Os)
 set(CXX_FLAGS -fno-rtti)