compiler: Rename misleading libcNeedsLibUnwind() function.

It's about libc++, not libc.

src/Compilation/Config.zig

@@ -313,7 +313,7 @@ pub fn resolve(options: Options) ResolveError!Config {
     };
 
     const link_libunwind = b: {
-        if (link_libcpp and target_util.libcNeedsLibUnwind(target)) {
+        if (link_libcpp and target_util.libCxxNeedsLibUnwind(target)) {
             if (options.link_libunwind == false) return error.LibCppRequiresLibUnwind;
             break :b true;
         }

src/target.zig

@@ -23,7 +23,7 @@ pub fn osRequiresLibC(target: std.Target) bool {
     return target.os.requiresLibC();
 }
 
-pub fn libcNeedsLibUnwind(target: std.Target) bool {
+pub fn libCxxNeedsLibUnwind(target: std.Target) bool {
     return switch (target.os.tag) {
         .macos,
         .ios,