[adwaita-icon-theme] Avoid a hard dependency on gtk-update-icon-cache

[Jakub Steiner <jimmac src gnome org>]

commit 3227136e998ea655ed7d2b6b0be5909f6608da7b
Author: Kalev Lember <kalevlember gmail com>
Date:   Tue Oct 28 11:42:19 2014 +0100

    Avoid a hard dependency on gtk-update-icon-cache
    
    This makes is possible to build adwaita-icon-theme before gtk+ and
    avoids a circular dependency between those two modules.
    
    https://bugzilla.gnome.org/show_bug.cgi?id=739290

 Makefile.am  |    2 +-
 configure.ac |    3 ---
 2 files changed, 1 insertions(+), 4 deletions(-)
---
diff --git a/Makefile.am b/Makefile.am
index 7cf1a44..fed3972 100644
--- a/Makefile.am
+++ b/Makefile.am
@@ -99,7 +99,7 @@ install-data-local:
        fi
 
 install-data-hook:
-       if test -z "$(DESTDIR)" ; then \
+       if test -z "$(DESTDIR)" && test -n "$(GTK_UPDATE_ICON_CACHE)" ; then \
                $(GTK_UPDATE_ICON_CACHE) -q $(DESTDIR)$(themedir); \
        fi
 
diff --git a/configure.ac b/configure.ac
index ff67b7a..f0eb9e4 100644
--- a/configure.ac
+++ b/configure.ac
@@ -32,9 +32,6 @@ AC_SUBST([symbolic_render_sizes], [""])
 AC_SUBST([install_sizes], ["8x8 16x16 22x22 24x24 32x32 48x48 64x64 96x96 256x256"])
 
 AC_PATH_PROG(GTK_UPDATE_ICON_CACHE, gtk-update-icon-cache)
-if test -z "$GTK_UPDATE_ICON_CACHE"; then
-    AC_MSG_ERROR([Could not find gtk-update-icon-cache])
-fi
 
 # need git, icontool, and inkscape for rendering
 allow_rendering=yes