re PR libgomp/26175 (In gcc-4.2.0 libgomp/.../powerpc/futex.h SYS_futex undefined)

	PR libgomp/26175
	PR libgomp/26477
	* configure.ac: If neither --enable-linux-futex nor
	--disable-linux-futex is passed, determine the default by checking
	for compiling and/or running against NPTL.  With --enable-linux-futex,
	check if SYS_gettid and SYS_futex are defined.
	* configure: Rebuilt.

From-SVN: r114809