x86: Test if compiler supports -m16
-m16 option is available only since GCC 4.9.0 [1]. That causes a build
failure on centos-7 [2] that has GCC 4.8.5.
Fallback to -m32 if -m16 is not available.
1. http://gcc.gnu.org/bugzilla/show_bug.cgi?id=59672
2. https://gitlab.com/bonzini/kvm-unit-tests/-/jobs/755368387
Fixes: 2616ad934e2 ("x86: realmode: Workaround clang issues")
Reported-by: Roman Bolshakov <r.bolshakov@yadro.com>
[Commit message by Roman Bolshakov, patch redone. - Paolo]
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
diff --git a/x86/Makefile.common b/x86/Makefile.common
index 5567d66..b942086 100644
--- a/x86/Makefile.common
+++ b/x86/Makefile.common
@@ -72,7 +72,7 @@
$(CC) -m32 -nostdlib -o $@ -Wl,-m,elf_i386 \
-Wl,-T,$(SRCDIR)/$(TEST_DIR)/realmode.lds $^
-$(TEST_DIR)/realmode.o: bits = 16
+$(TEST_DIR)/realmode.o: bits = $(if $(call cc-option,-m16,""),16,32)
$(TEST_DIR)/kvmclock_test.elf: $(TEST_DIR)/kvmclock.o
