Fix .exe-related test failure on MinGW.

[Ralf Wildenhues]

Applied as obvious, fixing a failure of test 3 with M4=/bin/m4.exe
passed explicitly to configure.

Cheers,
Ralf

    Fix .exe-related test failure on MinGW.
    
    * tests/local.at (AT_CHECK_M4): Normalize `/bin/m4.exe' correctly
    for comparing warning output.

diff --git a/tests/local.at b/tests/local.at
index fce3eb3..33fbf05 100644
--- a/tests/local.at
+++ b/tests/local.at
@@ -107,6 +107,7 @@ m4_define([AT_CHECK_M4],
           m4_case([$4], [], [], [ignore], [ignore], [stderr]))
 m4_case([$4], [], [], [ignore], [],
 [AT_CHECK([[sed 's/^[^:]*m4: *\([^:]*:\) *\([0-9][0-9]*: \)/m4:\1\2/
+       s/^[^:]*m4\.exe: *\([^:]*:\) *\([0-9][0-9]*: \)/m4:\1\2/
        s/^\([^:]*:\) *\([0-9][0-9]*:\)[^:]*m4: /m4:\1\2 /
        s/: C\(annot open \)\([^`:]*\):/: c\1`\2'\'':/
        s/: include:\( cannot open\)/:\1/