[libc++] Make _LIBCPP_MAKE_OVERRIDABLE_FUNCTION_DETECTABLE a no-op on baremetal

Baremetal targets tend to use custom linker scripts, which may not
include the __lcxx_override section.

BUG=b:363082822

patch.cherry: false
patch.platforms: chromiumos
patch.version_range.from: 530567
patch.version_range.until: null

Change-Id: Ibfd20a98eddb655b90eda7c99e72bfc1f9613c69

Author: thughes

libcxx/src/include/overridable_function.h

@@ -63,7 +63,14 @@
 // want to be defining special sections inside user's executables which use our headers.
 //
 
-#if defined(_LIBCPP_OBJECT_FORMAT_MACHO)
+// Baremetal targets tend to use custom linker scripts, which may not include
+// the __lcxx_override section.
+#if defined(LIBCXXABI_BAREMETAL)
+
+#  define _LIBCPP_CAN_DETECT_OVERRIDDEN_FUNCTION 0
+#  define _LIBCPP_MAKE_OVERRIDABLE_FUNCTION_DETECTABLE /* nothing */
+
+#elif defined(_LIBCPP_OBJECT_FORMAT_MACHO)
 
 #  define _LIBCPP_CAN_DETECT_OVERRIDDEN_FUNCTION 1
 #  define _LIBCPP_MAKE_OVERRIDABLE_FUNCTION_DETECTABLE                                                                 \