builder: use .dylib for -shared builds in macOS

cmd/tools/vcreate.v

@@ -44,6 +44,7 @@ fn gen_gitignore(name string) string {
 		'main',
 		'$name',
 		'*.so',
+		'*.dylib',
 		'*.dll'
 	].join('\n')
 }

vlib/v/builder/cc.v

@@ -147,8 +147,12 @@ fn (mut v Builder) cc() {
 	if v.pref.is_shared {
 		linker_flags << '-shared'
 		a << '-fPIC' // -Wl,-z,defs'
+		$if macos {
+			v.pref.out_name += '.dylib'
+		} $else {
 			v.pref.out_name += '.so'
 		}
+	}
 	if v.pref.is_bare {
 		a << '-fno-stack-protector'
 		a << '-ffreestanding'