libstdc++, testsuite, Darwin : Adjust for names used in system headers.

libstdc++, testsuite, Darwin : Adjust for names used in system headers.

For all current Darwin SDKs inttypes.h has:
extern intmax_t imaxabs(intmax_t j);

So we need to exclude j from the defined test symbols.

libstdc++-v3/ChangeLog:

	* testsuite/17_intro/names.cc: Exclude j from the list
	of test symbols for Darwin.

(cherry picked from commit 6f4b0ff2b1fbd58669ae130387c7535110300c52)