[libc++] [test] Consistently use REQUIRES: has-unix-headers (llvm#94122)

There were 7 occurrences of `UNSUPPORTED: !has-unix-headers`, versus 212
occurrences of `REQUIRES: has-unix-headers`.

I don't completely understand how libc++ uses UNSUPPORTED versus
REQUIRES, but it seems better to be consistent, and to avoid the double
negation in "this is unsupported if we don't have unix headers".

(This came to my attention because of the single occurrence in
`libcxx/test/std`. Our MSVC-internal test harness isn't aware of lit
features, so we teach it to skip tests via the incredibly primitive
method of searching for specific comments, so I had to deal with this
comment inconsistency.)

Author: StephanTLavavej

libcxx/test/libcxx/assertions/modes/enabling_assertions_enables_extensive_mode.pass.cpp

@@ -11,7 +11,8 @@
 // hardening mode.
 
 // `check_assertion.h` is only available starting from C++11 and requires Unix headers and regex support.
-// UNSUPPORTED: c++03, !has-unix-headers, no-localization
+// REQUIRES: has-unix-headers
+// UNSUPPORTED: c++03, no-localization
 // The ability to set a custom abort message is required to compare the assertion message (which only happens in the
 // debug mode).
 // XFAIL: libcpp-hardening-mode=debug && availability-verbose_abort-missing

libcxx/test/libcxx/assertions/modes/override_with_debug_mode.pass.cpp

@@ -9,7 +9,8 @@
 // This test ensures that we can override any hardening mode with the debug mode on a per-TU basis.
 
 // `check_assertion.h` is only available starting from C++11 and requires Unix headers and regex support.
-// UNSUPPORTED: c++03, !has-unix-headers, no-localization
+// REQUIRES: has-unix-headers
+// UNSUPPORTED: c++03, no-localization
 // The ability to set a custom abort message is required to compare the assertion message.
 // XFAIL: availability-verbose_abort-missing
 // ADDITIONAL_COMPILE_FLAGS: -U_LIBCPP_HARDENING_MODE -D_LIBCPP_HARDENING_MODE=_LIBCPP_HARDENING_MODE_DEBUG

libcxx/test/libcxx/assertions/modes/override_with_extensive_mode.pass.cpp

@@ -9,7 +9,8 @@
 // This test ensures that we can override any hardening mode with the extensive hardening mode on a per-TU basis.
 
 // `check_assertion.h` is only available starting from C++11 and requires Unix headers and regex support.
-// UNSUPPORTED: c++03, !has-unix-headers, no-localization
+// REQUIRES: has-unix-headers
+// UNSUPPORTED: c++03, no-localization
 // The ability to set a custom abort message is required to compare the assertion message (which only happens in the
 // debug mode).
 // XFAIL: libcpp-hardening-mode=debug && availability-verbose_abort-missing

libcxx/test/libcxx/assertions/modes/override_with_fast_mode.pass.cpp

@@ -9,7 +9,8 @@
 // This test ensures that we can override any hardening mode with the fast mode on a per-TU basis.
 
 // `check_assertion.h` is only available starting from C++11 and requires Unix headers and regex support.
-// UNSUPPORTED: c++03, !has-unix-headers, no-localization
+// REQUIRES: has-unix-headers
+// UNSUPPORTED: c++03, no-localization
 // The ability to set a custom abort message is required to compare the assertion message (which only happens in the
 // debug mode).
 // XFAIL: libcpp-hardening-mode=debug && availability-verbose_abort-missing

libcxx/test/libcxx/assertions/modes/override_with_unchecked_mode.pass.cpp

@@ -9,7 +9,8 @@
 // This test ensures that we can override any hardening mode with the unchecked mode on a per-TU basis.
 
 // `check_assertion.h` is only available starting from C++11 and requires Unix headers and regex support.
-// UNSUPPORTED: c++03, !has-unix-headers, no-localization
+// REQUIRES: has-unix-headers
+// UNSUPPORTED: c++03, no-localization
 // ADDITIONAL_COMPILE_FLAGS: -U_LIBCPP_HARDENING_MODE -D_LIBCPP_HARDENING_MODE=_LIBCPP_HARDENING_MODE_NONE
 
 #include <cassert>

libcxx/test/libcxx/containers/sequences/deque/asan_caterpillar.pass.cpp

@@ -12,7 +12,8 @@
 // with origin in deque::__add_back_capacity.
 
 // `check_assertion.h` is only available starting from C++11 and requires Unix headers and regex support.
-// UNSUPPORTED: c++03, !has-unix-headers, no-localization
+// REQUIRES: has-unix-headers
+// UNSUPPORTED: c++03, no-localization
 
 #include <deque>
 #include <cstdio>

libcxx/test/std/algorithms/pstl.exception_handling.pass.cpp

@@ -9,7 +9,8 @@
 // UNSUPPORTED: c++03, c++11, c++14
 // UNSUPPORTED: no-exceptions
 // `check_assertion.h` requires Unix headers and regex support.
-// UNSUPPORTED: !has-unix-headers, no-localization
+// REQUIRES: has-unix-headers
+// UNSUPPORTED: no-localization
 
 // UNSUPPORTED: libcpp-has-no-incomplete-pstl