[xen staging] tools/tests/x86_emulator: fix build on clang-21

[patchbot@xxxxxxx]

commit 34e9c2151444ffc96f0be193445d3f6b146653d3
Author:     Edwin Török <edwin.torok@xxxxxxxxxx>
AuthorDate: Wed Mar 4 08:25:19 2026 +0100
Commit:     Jan Beulich <jbeulich@xxxxxxxx>
CommitDate: Wed Mar 4 08:25:19 2026 +0100

    tools/tests/x86_emulator: fix build on clang-21
    
    clang-21's built-in assembler is enabled by default, but it doesn't
    support some mnemonics:
    ```
    test_x86_emulator.c:2636:36: error: invalid instruction mnemonic 'fsaves'
     2636 |                        "fidivs %1\n\t"
    test_x86_emulator.c:2640:24: error: invalid instruction mnemonic 'frstors'
     2640 |         asm volatile ( "frstors %0" :: "m" (res[25]) : "memory" );
          |                        ^
    test_x86_emulator.c:4251:24: error: invalid instruction mnemonic 
'vpcmpestriq'
     4251 |                        put_insn(vpcmpestri,
          |                        ^
    ```
    
    Use the external assembler with Clang for consistency with GCC.
    
    Signed-off-by: Edwin Török <edwin.torok@xxxxxxxxxx>
    Acked-by: Jan Beulich <jbeulich@xxxxxxxx>
---
 tools/tests/x86_emulator/Makefile | 5 +++++
 1 file changed, 5 insertions(+)

diff --git a/tools/tests/x86_emulator/Makefile 
b/tools/tests/x86_emulator/Makefile
index e18725d0c3..5003c464f3 100644
--- a/tools/tests/x86_emulator/Makefile
+++ b/tools/tests/x86_emulator/Makefile
@@ -297,6 +297,11 @@ x86_emulate:
 
 HOSTCFLAGS-x86_64 := -fno-PIE
 $(call cc-option-add,HOSTCFLAGS-x86_64,HOSTCC,-no-pie)
+
+# clang's integrated as does not support some mnemonics:
+#  https://github.com/llvm/llvm-project/issues/183635
+$(call cc-option-add,HOSTCFLAGS-x86_64,HOSTCC,-no-integrated-as)
+
 HOSTCFLAGS += $(CFLAGS_xeninclude) -I. $(HOSTCFLAGS-$(XEN_COMPILE_ARCH))
 
 x86.h := $(addprefix $(XEN_ROOT)/tools/include/xen/asm/,\
--
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