build: Don't use JAVA_CPPFLAGS, FT2_CPPFLAGS everywhere when making .df files. *.cc -> *.df rule now stops build when it fails (as it should have done before). * libinterp/Makefile.am: Remove FONTCONFIG_CPPFLAGS, FT2_CPPFLAGS, JAVA_CPPFLAGS from defaulte *.cc -> *.df rule. Abort make if rule errors out. * libinterp/corefcn/module.mk: Add overriding *.cc -> *.df rule for files which use (FONTCONFIG|FT2)_CPPFLAGS. * libinterp/octave-value/module.mk: Add overriding *.cc -> *.df rule for files which use JAVA_CPPFLAGS.