tdf#115283: Avoid bashism

(We do require bash for other parts of the build, though, and have no
plans to change that. But let's make the bug reporter happy here.)

Change-Id: I4bcd3a86fb4e6f95d4eec8557faf359bf5549c03

configure.ac

@@ -168,7 +168,7 @@ if test "$enable_release_build" = "" -o "$enable_release_build" = "no"; then
 fi
 AC_MSG_RESULT([$PRODUCTNAME])
 AC_SUBST(PRODUCTNAME)
-PRODUCTNAME_WITHOUT_SPACES=${PRODUCTNAME// /}
+PRODUCTNAME_WITHOUT_SPACES=$(echo "$PRODUCTNAME" | sed 's/ //g')
 AC_SUBST(PRODUCTNAME_WITHOUT_SPACES)
 
 dnl ===================================================================