abicheck.sh portability

[Nick Schermer]

The lines below work fine under linux for xfconf, ${CC:-cc} is not
working, since on linux it requires cpp, if $CC is defined it won't
work either, so maybe we can use $CPP to override the default cpp?

${CPP:-cpp} -E -DINCLUDE_INTERNAL_SYMBOLS -DINCLUDE_VARIABLES
-DALL_FILES ${srcdir:-.}/xfconf.symbols | sed 's/ G_GNUC.*$//;s/
PRIVATE//;/^#.*$/d;/^$/d' | sort > expected-abi
nm -D -g -P .libs/libxfconf-0.so | awk '$2~/^[DRT]$/&&$1~/^[^_]/{print
$1}' | sort > actual-abi
diff -u expected-abi actual-abi && rm expected-abi actual-abi

Nick