build: add -Wexpansion-to-defined

This warning is included in -Wall by clang, but not by GCC (which only
enables it for -Wextra).  Include it in the list of warnings we enable
to minimize the differences between the compilers:

Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

diff --git a/configure b/configure
index 902653ae03e815b5ec0cf7dead99c10becf49ec0..dceeb72e5e9ad500fad962f9423d169f181d342f 100755 (executable)
--- a/configure
+++ b/configure
@@ -1583,7 +1583,7 @@ gcc_flags="-Wold-style-declaration -Wold-style-definition -Wtype-limits"
 gcc_flags="-Wformat-security -Wformat-y2k -Winit-self -Wignored-qualifiers $gcc_flags"
 gcc_flags="-Wno-missing-include-dirs -Wempty-body -Wnested-externs $gcc_flags"
 gcc_flags="-Wendif-labels -Wno-shift-negative-value $gcc_flags"
-gcc_flags="-Wno-initializer-overrides $gcc_flags"
+gcc_flags="-Wno-initializer-overrides -Wexpansion-to-defined $gcc_flags"
 gcc_flags="-Wno-string-plus-int $gcc_flags"
 # Note that we do not add -Werror to gcc_flags here, because that would
 # enable it for all configure tests. If a configure test failed due