Remove i386 and ppc code from os.h. Add comments from STRUCT_SIZE_LIMIT

Change-Id: Ibbd2e5a4da6fb67ed3161fb9653c613b0a9b0ba2
Signed-off-by: Lakshmi Shanmugam <lshanmug@in.ibm.com>

bundles/org.eclipse.swt/Eclipse SWT PI/cocoa/library/os.h

diff --git a/bundles/org.eclipse.swt/Eclipse SWT PI/cocoa/library/os.h b/bundles/org.eclipse.swt/Eclipse SWT PI/cocoa/library/os.h
index 6d71bb9..69ff811 100644
--- a/bundles/org.eclipse.swt/Eclipse SWT PI/cocoa/library/os.h
+++ b/bundles/org.eclipse.swt/Eclipse SWT PI/cocoa/library/os.h
@@ -35,26 +35,18 @@
 #define objc_msgSendSuper_bool objc_msgSendSuper
 
 #define objc_msgSend_floatret objc_msgSend_fpret
-#ifndef __i386__
-#define objc_msgSend_fpret objc_msgSend
-#endif
 
 /* The structure objc_super defines "class" in i386/ppc and "super_class" in x86_64 */
-#ifdef __i386__
-#define swt_super_class class
-#elif __ppc__
-#define swt_super_class class
-#elif __x86_64__
+#ifdef __x86_64__
 #define swt_super_class super_class
 #elif __arm64__
 #define swt_super_class super_class
 #endif
 
-#ifdef __i386__
-#define STRUCT_SIZE_LIMIT 8
-#elif __ppc__
-#define STRUCT_SIZE_LIMIT 4
-#elif __x86_64__
+/* STRUCT_SIZE_LIMIT is the maximum size of struct that can be returned using registers */
+/* When sizeof(struct) is greater than this limit, objc_msgSend*_stret call is used */
+/* objc_msgSend*_stret methods are not available on arm64 architecture, so objc_msgSend* calls are always used */
+#ifdef __x86_64__
 #define STRUCT_SIZE_LIMIT 16
 #elif __arm64__
 #define STRUCT_SIZE_LIMIT 64