[gspell] Revert "pkg-config file: remove exec_prefix, unused"

[Sébastien Wilmet <swilmet src gnome org>]

commit 8bc177554e68cd2c0c3f098a4f2b4e1d3a017caf
Author: Sébastien Wilmet <swilmet informatique-libre be>
Date:   Thu Aug 18 19:19:11 2022 +0200

    Revert "pkg-config file: remove exec_prefix, unused"
    
    This reverts commit 28b7e23f680e23c02ea63b5c0654eba43cad3091.
    
    I didn't know, but it's actually used. The generated *.pc file contains:
    
    libdir=${exec_prefix}/lib64
    
    This is not necessary with some other build systems.

 gspell.pc.in | 1 +
 1 file changed, 1 insertion(+)
---
diff --git a/gspell.pc.in b/gspell.pc.in
index 7fd0104..3252f08 100644
--- a/gspell.pc.in
+++ b/gspell.pc.in
@@ -1,4 +1,5 @@
 prefix=@prefix@
+exec_prefix=@exec_prefix@
 libdir=@libdir@
 includedir=@includedir@