Make ENABLE_WERROR actually work

This change explicitly adds -Werror to the CFLAGS.

Due to the way that the ADD_C_FLAG_IF_SUPPORTED() macro was mangling the
flag name to convert it into a define name, any warning that had a dash
in its name was not being correctly enabled. Additionally, any flag that
is enabled implicitly by the compiler (like -Wunused-result and
-Wdeprecated-declarations) would not cause an error unless they were
explicitly enabled with the ENABLE_WARNINGS() macro.

cmake/Modules/AddCFlagIfSupported.cmake

@@ -7,7 +7,8 @@ INCLUDE(CheckCCompilerFlag)
 
 MACRO(ADD_C_FLAG _FLAG)
 	STRING(TOUPPER ${_FLAG} UPCASE)
-	STRING(REGEX REPLACE "^-" "" UPCASE_PRETTY ${UPCASE})
+	STRING(REGEX REPLACE "[-=]" "_" UPCASE_PRETTY ${UPCASE})
+	STRING(REGEX REPLACE "^_+" "" UPCASE_PRETTY ${UPCASE_PRETTY})
 	CHECK_C_COMPILER_FLAG(${_FLAG} IS_${UPCASE_PRETTY}_SUPPORTED)
 
 	IF(IS_${UPCASE_PRETTY}_SUPPORTED)
@@ -19,7 +20,8 @@ ENDMACRO()
 
 MACRO(ADD_C_FLAG_IF_SUPPORTED _FLAG)
 	STRING(TOUPPER ${_FLAG} UPCASE)
-	STRING(REGEX REPLACE "^-" "" UPCASE_PRETTY ${UPCASE})
+	STRING(REGEX REPLACE "[-=]" "_" UPCASE_PRETTY ${UPCASE})
+	STRING(REGEX REPLACE "^_+" "" UPCASE_PRETTY ${UPCASE_PRETTY})
 	CHECK_C_COMPILER_FLAG(${_FLAG} IS_${UPCASE_PRETTY}_SUPPORTED)
 
 	IF(IS_${UPCASE_PRETTY}_SUPPORTED)

cmake/Modules/EnableWarnings.cmake

 MACRO(ENABLE_WARNINGS flag)
-	IF(ENABLE_WERROR)
-		ADD_C_FLAG_IF_SUPPORTED(-Werror=${flag})
-	ELSE()
-		ADD_C_FLAG_IF_SUPPORTED(-W${flag})
-	ENDIF()
+	ADD_C_FLAG_IF_SUPPORTED(-W${flag})
 ENDMACRO()
 
 MACRO(DISABLE_WARNINGS flag)
 	ADD_C_FLAG_IF_SUPPORTED(-Wno-${flag})
-	IF(ENABLE_WERROR)
-		ADD_C_FLAG_IF_SUPPORTED(-Wno-error=${flag})
-	ENDIF()
 ENDMACRO()
+
+IF(ENABLE_WERROR)
+	ADD_C_FLAG_IF_SUPPORTED(-Werror)
+ENDIF()