Rename objc to objective-c

Fixes: #495
Co-Authored-By: Beyar <beyar-123@live.com>

o/objective-c.m

@@ -0,0 +1,14 @@
+/*
+ Build on OS X: 
+ clang -framework Foundation -fobjc-arc objc.m -o objc
+ 
+ Build on Linux with GNUstep:
+ clang `gnustep-config --objc-flags` `gnustep-config --base-libs` -fobjc-nonfragile-abi -fobjc-arc objc.m -o objc
+ */
+
+#import <Foundation/Foundation.h>
+
+int main(void)
+{
+    NSLog(@"Hello World");
+}