Remove duplicate CMAKE_C_FLAGS inside CMAKE_C_FLAGS_DEBUG.

- For Debug builds, CMake uses concatenated
  CMAKE_C_FLAGS and CMAKE_C_FLAGS_DEBUG
- This reverts commit 291f7122.

CMakeLists.txt

@@ -98,8 +98,8 @@ IF (MSVC)
    # Precompiled headers
 
 ELSE ()
-	SET(CMAKE_C_FLAGS_DEBUG "-O0 -g ${CMAKE_C_FLAGS}")
 	SET(CMAKE_C_FLAGS "-O2 -g -D_GNU_SOURCE -Wall -Wextra -Wno-missing-field-initializers -Wstrict-aliasing=2 -Wstrict-prototypes -Wmissing-prototypes ${CMAKE_C_FLAGS}")
+	SET(CMAKE_C_FLAGS_DEBUG "-O0 -g")
 	IF (MINGW) # MinGW always does PIC and complains if we tell it to
 		STRING(REGEX REPLACE "-fPIC" "" CMAKE_SHARED_LIBRARY_C_FLAGS "${CMAKE_SHARED_LIBRARY_C_FLAGS}")
 	ELSE ()