[gsound/wip/hadess/fix-automake] build: Fix automake variables usage

[Bastien Nocera <hadess src gnome org>]

commit e5b8a20c94388f421ff855154a198f131eec6010
Author: Bastien Nocera <hadess hadess net>
Date:   Thu Jul 22 13:42:45 2021 +0200

    build: Fix automake variables usage
    
    The variables should be used with $() not ${} otherwise we might see
    automake choking on the variable substitution:
    gsound/Makefile.am: installing 'build-aux/depcomp'
    Unescaped left brace in regex is passed through in regex; marked by <-- HERE in m/^${ <-- HERE 
abs_top_builddir}/gsound$/ at /usr/bin/automake line 5755.
    autoreconf: automake failed with exit status: 255

 tools/Makefile.am | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)
---
diff --git a/tools/Makefile.am b/tools/Makefile.am
index 11f8e01..a81c296 100644
--- a/tools/Makefile.am
+++ b/tools/Makefile.am
@@ -8,7 +8,7 @@ bin_PROGRAMS = gsound-play
 gsound_play_SOURCES = gsound-play.vala
 
 gsound_play_VALAFLAGS = \
-    --vapidir ${abs_top_builddir}/gsound \
+    --vapidir $(abs_top_builddir)/gsound \
     --pkg gsound \
     ${NULL}
 
@@ -18,7 +18,7 @@ gsound_play_CPPFLAGS = \
     ${NULL}
 
 gsound_play_LDFLAGS = \
-    ${top_builddir}/gsound/libgsound.la \
+    $(top_builddir)/gsound/libgsound.la \
     ${GSOUND_LIBS} \
     ${NULL}