http://git.savannah.gnu.org/cgit/bison.git/commit/?id=4ad3921d3be296de6a2b3c5fe0e18136d53ba06d

--- a/tests/synclines.at
+++ b/tests/synclines.at
@@ -71,7 +71,9 @@ AT_CHECK([[test "`cat stdout`" = 'syncline.c:1: @%:@error "1"' || exit 77]])
 AT_DATA([[input.y]], [$2])
 AT_BISON_CHECK([-o input.c input.y])
 AT_SYNCLINES_COMPILE([input.c])
-AT_CHECK([cat stdout], 0, [$3])
+# GCC 4.5 tells you the function within which #error appears, but
+# previous versions of gcc do not.
+AT_CHECK([grep -v ': In function ' stdout], 0, [$3])
 AT_CLEANUP
 ])
 

patch the testsuite to avoid autotools at emerge time
http://bugs.gentoo.org/331577

--- a/tests/testsuite
+++ b/tests/testsuite
@@ -15299,9 +15299,9 @@
 
 
 { set +x
-$as_echo "$at_srcdir/synclines.at:84: cat stdout"
+$as_echo "$at_srcdir/synclines.at:84: grep -v ': In function ' stdout"
 at_fn_check_prepare_trace "synclines.at:84"
-( $at_check_trace; cat stdout
+( $at_check_trace; grep -v ': In function ' stdout
 ) >>"$at_stdout" 2>>"$at_stderr"
 at_status=$? at_failed=false
 $at_check_filter
@@ -15535,9 +15535,9 @@
 
 
 { set +x
-$as_echo "$at_srcdir/synclines.at:101: cat stdout"
+$as_echo "$at_srcdir/synclines.at:101: grep -v ': In function ' stdout"
 at_fn_check_prepare_trace "synclines.at:101"
-( $at_check_trace; cat stdout
+( $at_check_trace; grep -v ': In function ' stdout
 ) >>"$at_stdout" 2>>"$at_stderr"
 at_status=$? at_failed=false
 $at_check_filter
@@ -15774,9 +15774,9 @@
 
 
 { set +x
-$as_echo "$at_srcdir/synclines.at:121: cat stdout"
+$as_echo "$at_srcdir/synclines.at:121: grep -v ': In function ' stdout"
 at_fn_check_prepare_trace "synclines.at:121"
-( $at_check_trace; cat stdout
+( $at_check_trace; grep -v ': In function ' stdout
 ) >>"$at_stdout" 2>>"$at_stderr"
 at_status=$? at_failed=false
 $at_check_filter
@@ -16009,9 +16009,9 @@
 
 
 { set +x
-$as_echo "$at_srcdir/synclines.at:144: cat stdout"
+$as_echo "$at_srcdir/synclines.at:144: grep -v ': In function ' stdout"
 at_fn_check_prepare_trace "synclines.at:144"
-( $at_check_trace; cat stdout
+( $at_check_trace; grep -v ': In function ' stdout
 ) >>"$at_stdout" 2>>"$at_stderr"
 at_status=$? at_failed=false
 $at_check_filter
@@ -16243,9 +16243,9 @@
 
 
 { set +x
-$as_echo "$at_srcdir/synclines.at:163: cat stdout"
+$as_echo "$at_srcdir/synclines.at:163: grep -v ': In function ' stdout"
 at_fn_check_prepare_trace "synclines.at:163"
-( $at_check_trace; cat stdout
+( $at_check_trace; grep -v ': In function ' stdout
 ) >>"$at_stdout" 2>>"$at_stderr"
 at_status=$? at_failed=false
 $at_check_filter