[PATCH for-4.15] x86/efi: enable MS ABI attribute on clang

[Roger Pau Monne <roger.pau@citrix.com>]

Or else the EFI service calls will use the wrong calling convention.

The __ms_abi__ attribute is available on all supported versions of
clang.

Signed-off-by: Roger Pau Monné <roger.pau@citrix.com>
---
Cc: Ian Jackson <iwj@xenproject.org>

Without this a Xen built with clang won't be able to correctly use the
EFI services, leading to weird messages from the firmware and crashes.
The impact of this fix for GCC users is exactly 0, and will fix the
build on clang.

The biggest fallout from this could be using the attribute on a
compiler that doesn't support it, which would translate into a build
failure, but the gitlab tests have shown no issues.
---
 xen/include/asm-x86/x86_64/efibind.h | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/xen/include/asm-x86/x86_64/efibind.h b/xen/include/asm-x86/x86_64/efibind.h
index b013db175d..ddcfae07ec 100644
--- a/xen/include/asm-x86/x86_64/efibind.h
+++ b/xen/include/asm-x86/x86_64/efibind.h
@@ -172,7 +172,7 @@ typedef uint64_t   UINTN;
 #ifndef EFIAPI                  // Forces EFI calling conventions reguardless of compiler options
     #ifdef _MSC_EXTENSIONS
         #define EFIAPI __cdecl  // Force C calling convention for Microsoft C compiler
-    #elif __GNUC__ > 4 || (__GNUC__ == 4 && __GNUC_MINOR__ >= 4)
+    #elif __clang__ || __GNUC__ > 4 || (__GNUC__ == 4 && __GNUC_MINOR__ >= 4)
         #define EFIAPI __attribute__((__ms_abi__))  // Force Microsoft ABI
     #else
         #define EFIAPI          // Substitute expresion to force C calling convention
-- 
2.29.2