CMakeLists.txt: enable -Wall and disable some resulting warnings

CMakeLists.txt

@@ -102,10 +102,10 @@ endif ()
 if (MSVC)
     add_definitions(/TP -D_CRT_SECURE_NO_WARNINGS /wd4065 /wd4018 /wd4533 /wd4244 /wd4102)
 else ()
-    add_definitions(-std=gnu99 -Wno-unused-value -Wno-parentheses -Wno-switch -Wredundant-decls)
+    add_definitions(-std=gnu99 -Wall -Wno-unused-value -Wno-parentheses -Wno-switch -Wredundant-decls)
 
     if (NOT CMAKE_C_COMPILER_ID STREQUAL "PathScale")
-        add_definitions(-Werror=implicit-function-declaration -Wno-switch-enum)
+        add_definitions(-Werror=implicit-function-declaration -Wno-switch-enum -Wno-unused-function -Wno-initializer-overrides)
     endif ()
 endif ()