fix(configure): Correctly detect visibility("hidden") support on Darwin

[mbektchiev]

When performing this test on macOS High Sierra:

echo 'int __attribute__ ((visibility ("hidden"))) foo (void) { return 1  ; }' > conftest.c
gcc -Werror -S conftest.c -o conftest.s;
cat conftest.s

I get the following output:

	.section	__TEXT,__text,regular,pure_instructions
	.macosx_version_min 10, 13
	.private_extern	_foo            ## -- Begin function foo
	.globl	_foo
	.p2align	4, 0x90
_foo:                                   ## @foo
	.cfi_startproc
## %bb.0:
	pushq	%rbp
	.cfi_def_cfa_offset 16
	.cfi_offset %rbp, -16
	movq	%rsp, %rbp
	.cfi_def_cfa_register %rbp
	movl	$1, %eax
	popq	%rbp
	retq
	.cfi_endproc
                                        ## -- End function

.subsections_via_symbols

$ gcc -v
Configured with: --prefix=/Applications/Xcode.app/Contents/Developer/usr --with-gxx-include-dir=/usr/include/c++/4.2.1
Apple LLVM version 10.0.0 (clang-1000.11.45.5)
Target: x86_64-apple-darwin17.7.0
Thread model: posix
InstalledDir: /Applications/Xcode.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/bin

[tromey]

Thank you.