Add -std=c99 for C-Hashmap

GCC on CentOS will default to C90, it seems. This means it needs C99
explicitly specified for C-Hashmap, or it will fail on using a variable
declaration in a for-loop.

desktop_version/CMakeLists.txt

@@ -318,6 +318,9 @@ else()
     # Disable RTTI
     string(REPLACE "-frtti" "" CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS}")
     set_source_files_properties(${VVV_CXX_SRC} PROPERTIES COMPILE_FLAGS -fno-rtti)
+
+    # Dependencies (as needed)
+    set_source_files_properties(${CHM_SRC} PROPERTIES COMPILE_FLAGS -std=c99)
 endif()
 
 # Unfortunately, it doesn't seem like distros package LodePNG