qemu: fix the build with clang on powerpc

Workaround the lack the of _CALL_SYSV and build with -O0;
-O1 causes linking errors and -O2 segfaults.

Input by Brad (maintainer)

emulators/qemu/Makefile

@@ -1,4 +1,4 @@
-# $OpenBSD: Makefile,v 1.194 2020/04/04 08:36:55 ajacoutot Exp $
+# $OpenBSD: Makefile,v 1.195 2020/04/23 04:30:35 cwen Exp $
 
 ONLY_FOR_ARCHS=	aarch64 amd64 arm i386 powerpc sparc64
 
@@ -106,6 +106,11 @@ CONFIGURE_ARGS+=--disable-debug-info
 
 TEST_TARGET=	check
 
+# XXX Optimizer bug, using -O2 causes segfaults, -O1 linking errors
+.if ${MACHINE_ARCH:Mpowerpc}
+CFLAGS +=	-O0
+.endif
+
 post-install:
 	${INSTALL_DATA_DIR} ${PREFIX}/share/examples/qemu
 	${INSTALL_SCRIPT} ${FILESDIR}/qemu-ifup \

emulators/qemu/patches/patch-tcg_ppc_tcg-target_inc_c

@@ -0,0 +1,19 @@
+$OpenBSD: patch-tcg_ppc_tcg-target_inc_c,v 1.6 2020/04/23 04:30:35 cwen Exp $
+
+Workaround the lack of _CALL_SYSV with clang on powerpc
+
+Index: tcg/ppc/tcg-target.inc.c
+--- tcg/ppc/tcg-target.inc.c.orig
++++ tcg/ppc/tcg-target.inc.c
+@@ -25,6 +25,11 @@
+ #include "elf.h"
+ #include "tcg-pool.inc.c"
+ 
++/* clang does not define _CALL_* */
++#if defined __clang__ && defined __ELF__
++#define _CALL_SYSV 1
++#endif
++
+ #if defined _CALL_DARWIN || defined __APPLE__
+ #define TCG_TARGET_CALL_DARWIN
+ #endif