[PATCH] maint: fix operator precedence in mbrtowc test

[Daiki Ueno]

This is a fix for test breakage introduced by commit 45228d96; the
equality expression must be parenthesized when negated with '!',
otherwise we always get:

  test-mbrtowc.c:49: assertion 'ret == (size_t)(-2)' failed

* m4/mbrtowc.m4 (gl_MBRTOWC_EMPTY_INPUT): Negate the entire expression.
* m4/mbrlen.m4 (gl_MBRLEN_EMPTY_INPUT): Likewise.
---
 m4/mbrlen.m4  | 2 +-
 m4/mbrtowc.m4 | 2 +-
 2 files changed, 2 insertions(+), 2 deletions(-)

diff --git a/m4/mbrlen.m4 b/m4/mbrlen.m4
index 42eb61a..68d7b91 100644
--- a/m4/mbrlen.m4
+++ b/m4/mbrlen.m4
@@ -253,7 +253,7 @@ changequote([,])dnl
            int
            main (void)
            {
-             return ! mbrlen ("", 0, &mbs) == (size_t) -2;
+             return mbrlen ("", 0, &mbs) != (size_t) -2;
            }]])],
         [gl_cv_func_mbrlen_empty_input=yes],
         [gl_cv_func_mbrlen_empty_input=no],
diff --git a/m4/mbrtowc.m4 b/m4/mbrtowc.m4
index deb9f06..be2e9d6 100644
--- a/m4/mbrtowc.m4
+++ b/m4/mbrtowc.m4
@@ -569,7 +569,7 @@ changequote([,])dnl
            int
            main (void)
            {
-             return ! mbrtowc (&wc, "", 0, &mbs) == (size_t) -2;
+             return mbrtowc (&wc, "", 0, &mbs) != (size_t) -2;
            }]])],
         [gl_cv_func_mbrtowc_empty_input=yes],
         [gl_cv_func_mbrtowc_empty_input=no],
-- 
2.5.0