configure: Fix -lm test, so that tools can be compiled on hosts that require -lm
The existing test whether "-lm" needs to be included or not is
insufficient as it reports false negative on Fedora20/ppc64.
This happens because sin(0.0) is a constant value which compiler
can safely throw away and therefore there is no need to add "-lm".
As the result, qemu-nbd/qemu-io/qemu-img tools cannot compile.
This adds a global variable and uses it in the test to prevent
from optimization.
Signed-off-by: Alexey Kardashevskiy <aik@ozlabs.ru>
[Use Peter's improvement on the test to fool LTO, and remove the
now useless -lm addition in Makefile.target. - Paolo]
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
diff --git a/configure b/configure
index 23ecb37..ed41eda 100755
--- a/configure
+++ b/configure
@@ -3453,7 +3453,7 @@
# Do we need libm
cat > $TMPC << EOF
#include <math.h>
-int main(void) { return isnan(sin(0.0)); }
+int main(int argc, char **argv) { return isnan(sin((double)argc)); }
EOF
if compile_prog "" "" ; then
:
