Merge pull request swiftlang#31562 from compnerd/increased-visibility

Runtime: simplify `SWIFT_LIBRARY_VISIBILITY`

Author: compnerd

stdlib/public/SwiftShims/Visibility.h

@@ -116,19 +116,6 @@
 #endif
 
 
-#ifndef SWIFT_GNUC_PREREQ
-# if defined(__GNUC__) && defined(__GNUC_MINOR__) && defined(__GNUC_PATCHLEVEL__)
-#  define SWIFT_GNUC_PREREQ(maj, min, patch) \
-    ((__GNUC__ << 20) + (__GNUC_MINOR__ << 10) + __GNUC_PATCHLEVEL__ >= \
-     ((maj) << 20) + ((min) << 10) + (patch))
-# elif defined(__GNUC__) && defined(__GNUC_MINOR__)
-#  define SWIFT_GNUC_PREREQ(maj, min, patch) \
-    ((__GNUC__ << 20) + (__GNUC_MINOR__ << 10) >= ((maj) << 20) + ((min) << 10))
-# else
-#  define SWIFT_GNUC_PREREQ(maj, min, patch) 0
-# endif
-#endif
-
 /// Attributes for runtime-stdlib interfaces.
 /// Use these for C implementations that are imported into Swift via SwiftShims
 /// and for C implementations of Swift @_silgen_name declarations
@@ -151,9 +138,8 @@
 
 // Match the definition of LLVM_LIBRARY_VISIBILITY from LLVM's
 // Compiler.h. That header requires C++ and this needs to work in C.
-#if (__has_attribute(visibility) || SWIFT_GNUC_PREREQ(4, 0, 0)) &&              \
-    !defined(__MINGW32__) && !defined(__CYGWIN__) && !defined(_WIN32)
-#define SWIFT_LIBRARY_VISIBILITY __attribute__ ((visibility("hidden")))
+#if __has_attribute(visibility) && (defined(__ELF__) || defined(__MACH__))
+#define SWIFT_LIBRARY_VISIBILITY __attribute__ ((__visibility__("hidden")))
 #else
 #define SWIFT_LIBRARY_VISIBILITY
 #endif