6079 libdisasm doesn't enable C99MODE properly

@@ -32,7 +32,5 @@
 
 INSTALL_DEPS_library = $(ROOTLINKS64) $(ROOTLINT64) $(ROOTLIBS64)
 INSTALL_DEPS_standalone = $(ROOTLIBS64)
 
 include ../Makefile.targ
-
-C99MODE = $(C99_ENABLE)