compilerSupportsFlag(): remove bogus .o suffix from test executables

this function does not just compile, but it also links, so the output
file should have no object file extension.

Change-Id: I65dd9bd334478545ceeabe9d1aacb44d9583cdd7
Reviewed-by: Joerg Bornemann <joerg.bornemann@theqtcompany.com>

configure

@@ -357,12 +357,12 @@ compilerSupportsFlag()
 int main() { return 0; }
 EOF
     if [ "$OPT_VERBOSE" = "yes" ]; then
-        "$@" -o conftest-out.o conftest.cpp
+        "$@" -o conftest-out conftest.cpp
     else
-        "$@" -o conftest-out.o conftest.cpp >/dev/null 2>&1
+        "$@" -o conftest-out conftest.cpp >/dev/null 2>&1
     fi
     ret=$?
-    rm -f conftest.cpp conftest-out.o
+    rm -f conftest.cpp conftest-out
     return $ret
 }