Skip stdlib tests on macOS

I don't fully understand what's going on here (Claude pretends to but I
doubt it) but there are bizarre errors without a proper compile commands
database here that seem entirely macOS specific. They seem to be due to
using conda's compilers and not the one that ships with xcode but we
want to support that use case both for the CI but also in general. Let's
ignore this test therefore. The other integration test already tests a
lot of stuff.

Author: saraedum

test/integration.cpp

@@ -7,7 +7,19 @@
 
 using namespace cppast;
 
-TEST_CASE("stdlib", "[.][integration]")
+// On macOS with conda's libclang/libc++, the bare-config path lacks the
+// implicit toolchain context (target predicates, _LIBCPP_* feature macros)
+// that the (conda) clang driver normally injects. Without it, libclang
+// mis-handles libc++ constructs like _LIBCPP_HIDE_FROM_ABI's abi_tag
+// attribute. The companion "cppast" integration test (which uses
+// compile_commands and therefore gets the full flag set) is unaffected.
+#if defined(__APPLE__)
+#    define CPPAST_STDLIB_TAG "[.][!mayfail][integration]"
+#else
+#    define CPPAST_STDLIB_TAG "[.][integration]"
+#endif
+
+TEST_CASE("stdlib", CPPAST_STDLIB_TAG)
 {
     auto code = R"(
 // list of headers from: http://en.cppreference.com/w/cpp/header