Move OPTNONE macro to eficompiler.h

This is also useful in downstream projects so add it
to public header

Signed-off-by: Callum Farmer <gmbr3@opensuse.org>

apps/debughook.c

@@ -37,13 +37,7 @@ GetVariable(CHAR16 *var, UINT8 **data, UINTN *len, EFI_GUID owner)
 EFI_GUID DUMMY_GUID =
 {0x55aad538, 0x8f82, 0x4e2a, {0xa4,0xf0,0xbe, 0x59, 0x13, 0xb6, 0x5f, 0x1e}};
 
-#if defined(__clang__)
-# define _OPTNONE __attribute__((optnone))
-#else
-# define _OPTNONE __attribute__((__optimize__("0")))
-#endif
-
-static _OPTNONE void
+static EFI_OPTNONE void
 DebugHook(void)
 {
 	EFI_GUID guid = DUMMY_GUID;

inc/eficompiler.h

@@ -28,6 +28,16 @@ Abstract:
 #endif
 #endif
 
+#ifdef _MSC_EXTENSIONS
+#define EFI_OPTNONE
+#else
+#ifdef __clang__
+#define EFI_OPTNONE __attribute__((optnone))
+#else
+#define EFI_OPTNONE __attribute__((__optimize__("0")))
+#endif
+#endif
+
 #ifdef _MSC_EXTENSIONS
 #define ALIGN(x) __declspec(align(x))
 #else