mksigtab.sh: skip signals defined as other signals

    
    Fixes Solaris build.
    
    Patch by Rainer Orth.
    
    Reviewed-on: https://go-review.googlesource.com/37587

From-SVN: r245794

gcc/go/gofrontend/MERGE

-e1502234b5011a1ab859519f1f217dbf4369ec9b
+a4f445e18fb06a032a4399859f432e03245f1a7d
 
 The first line of this file holds the git revision number of the last
 merge done from the gofrontend repository.

libgo/mksigtab.sh

@@ -56,7 +56,8 @@ echo '	_SIGSYS:    {_SigThrow, "SIGSYS: bad system call"},'
 # Handle signals that are not supported on all systems.
 
 checksig() {
-    if grep "const $1 = " gen-sysinfo.go >/dev/null 2>&1; then
+    if grep "const $1 = " gen-sysinfo.go >/dev/null 2>&1 \
+	&& ! grep "const $1 = _SIG" gen-sysinfo.go > /dev/null 2>&1; then
 	echo "	$1: $2,"
     fi
 }