[gimp/wip/Jehan/incremental-win-installer-improvements] Better libaa detection!

[Jehan <jehanp src gnome org>]

commit 50426d80e98aad25f374931d2282f7443b4e1f8e
Author: Jehan <jehan girinstud io>
Date:   Sun May 16 17:57:44 2021 +0200

    Better libaa detection!

 build/windows/gitlab-ci/build-gimp-msys2.sh |  1 -
 configure.ac                                | 21 +++++++++++++++------
 2 files changed, 15 insertions(+), 7 deletions(-)
---
diff --git a/build/windows/gitlab-ci/build-gimp-msys2.sh b/build/windows/gitlab-ci/build-gimp-msys2.sh
index 29c02604c3..898e590308 100644
--- a/build/windows/gitlab-ci/build-gimp-msys2.sh
+++ b/build/windows/gitlab-ci/build-gimp-msys2.sh
@@ -102,7 +102,6 @@ ccache --show-stats
 
 mkdir "_build${ARTIFACTS_SUFFIX}"
 cd "_build${ARTIFACTS_SUFFIX}"
-export AA_LIBS=`aalib-config --libs`
 ../autogen.sh --prefix="${GIMP_PREFIX}" --enable-windows-installer \
               --with-directx-sdk="${MSYS2_PREFIX}" \
               ${GIMP_OPTIONS}
diff --git a/configure.ac b/configure.ac
index 3fb9d1b03f..7f50fe2bcc 100644
--- a/configure.ac
+++ b/configure.ac
@@ -1656,16 +1656,25 @@ AC_SUBST(MNG_CFLAGS)
 AC_ARG_WITH(aa,  [  --without-aa            do not build the AA plug-in])
 
 have_libaa=no
-if test "x$with_aa" != xno && test -z "$AA_LIBS"; then
+if test "x$with_aa" != xno; then
   have_libaa=yes
+  # First case if manually set, use the AA_LIBS environment variable.
+  if test -z "$AA_LIBS"; then
+    # Otherwise try the aalib-config script.
+    AA_LIBS=`aalib-config --libs`
+    if test -z "$AA_LIBS"; then
+      # Just try -laa.
+      AA_LIBS='-laa'
+    fi
+  fi
   AC_CHECK_LIB(aa, aa_printf,
-    [AC_CHECK_HEADER(aalib.h,
-      FILE_AA='file-aa$(EXEEXT)'; AA_LIBS='-laa',
+    [AC_CHECK_HEADER(aalib.h,,
       [have_libaa="no (AA header file not found)"])],
     [have_libaa="no (AA library not found)"])
-elif test -n "$AA_LIBS"; then
-  have_libaa=yes
-  FILE_AA='file-aa$(EXEEXT)'
+
+  if test "$have_libaa" = yes; then
+    FILE_AA='file-aa$(EXEEXT)'
+  fi
 fi
 
 AC_SUBST(FILE_AA)