Detect broken ptrace in gdb_skip_float_test

Detect broken ptrace in gdb_skip_float_test

We recently found a ARM kernel ptrace bug
http://lists.infradead.org/pipermail/linux-arm-kernel/2016-May/431962.html
Details can be found in the comment in gdb_skip_float_test.  We can
skip floating point tests if the kernel bug is detected.

This patch adds more code in gdb_skip_float_test to detect the broken
ptrace on arm-linux.  Such detection should be done at the beginning
of the test, because it starts a fresh GDB, so change the test cases
to invoke gdb_skip_float_test at the beginning of test, and use its
return value afterwards.

Since gdb_skip_float_test becomes a gdb_caching_proc, so it can't
have an argument, this patch also removes argument "msg", which isn't
useful.

gdb/testsuite:

2016-09-02  Yao Qi  <yao.qi@linaro.org>

	* gdb.arch/arm-neon.exp: Skip it if gdb_skip_float_test returns
	true.
	* gdb.base/call-ar-st.exp: Invoke gdb_skip_float_test.
	* gdb.base/call-rt-st.exp: Likewise.
	* gdb.base/call-sc.exp: Invoke gdb_skip_float_test and use its
	return value instead of gdb,skip_float_test.
	* gdb.base/callfuncs.exp: Invoke gdb_skip_float_test.
	(do_function_calls): Use its return value instead of
	gdb,skip_float_test.
	* gdb.base/finish.exp: Likewise.
	* gdb.base/funcargs.exp: Likewise.
	* gdb.base/return.exp: Likewise.
	* gdb.base/return2.exp: Likewise.
	* gdb.base/varargs.exp: Likewise.
	* lib/gdb.exp (gdb_skip_float_test): Change it to
	gdb_caching_proc.  Detect the broken ptrace on arm-linux.