configury : Fix LEB128 support for non-GNU assemblers.

configury : Fix LEB128 support for non-GNU assemblers.

The current configuration test for LEB128 support in the assembler is
(a) specific to GNU assemblers and (b) only checks that the directives
are accepted, not that they give correct output.

The patch extends the asm test to cover one failure case present in
assemblers based off an older version of GAS (where a 64 bit value with
the MSB set presented to a .uleb128 directive causes a fail).

The test is now generalized such that it does not make use of any
specific test for assembler source/version, but checks that the output
is as expected.  We cater for scanning the object with objdump (either
binutils or LLVM) or Darwin otool.

gcc/ChangeLog:

	* configure.ac (check leb128 support): Check that assemblers both
	accept the LEB128 directives and also give the expected output.
	Add a test for uleb128 with the MSB set for a 64 bit value.
	* configure: Regenerated.