gcore: quote PKGVERSION

Same as 3bed686102. I didn't hit an issue
here -- I think because my /bin/sh is dash and gdb-add-index has a /bin/sh
shebang, while gcore uses bash, but it's still worth fixing (we certainly
do NOT want this to be an array).

Bug: https://sourceware.org/bugzilla/show_bug.cgi?id=32325

gdb/gcore-1.in

@@ -20,8 +20,8 @@
 # It starts up gdb, attaches to the given PID and invokes the gcore command.
 #
 
-PKGVERSION=@PKGVERSION@
-VERSION=@VERSION@
+PKGVERSION="@PKGVERSION@"
+VERSION="@VERSION@"
 
 # Need to check for -o option, but set default basename to "core".
 prefix=core