the test written there

if test "x$gp_galp_check = xC3\ \:\ C4"; then

always evaluates to true.
It is meant to check whether gp_galp_check (which may be empty) equals the string
"C3 : C4"

CC: @embray @kiwifb @isuruf @videlec

Component: build: configure

Author: Dima Pasechnik

Branch/Commit: 7d01e58

Reviewer: Isuru Fernando

Issue created by migration from https://trac.sagemath.org/ticket/28405