[gthumb] configure: Clear out ldflags before ac_check_lib() calls

[Paolo Bacchilega <paobac src gnome org>]

commit 70fd934cb2d51a582589fc93c22b3d0e2cfdf2d4
Author: Kalev Lember <kalevlember gmail com>
Date:   Thu Apr 16 13:00:55 2015 +0200

    configure: Clear out ldflags before ac_check_lib() calls
    
    This fixes the Fedora 23 build where the cflags and ldflags have to
    match. Otherwise, if ac_check_lib checks throw away cflags but use
    ldflags, the checks fail with linker errors.
    
    https://bugzilla.gnome.org/show_bug.cgi?id=747982

 configure.ac |   12 ++++++++++++
 1 files changed, 12 insertions(+), 0 deletions(-)
---
diff --git a/configure.ac b/configure.ac
index 7890d61..db67766 100644
--- a/configure.ac
+++ b/configure.ac
@@ -177,11 +177,15 @@ AC_SUBST(GTHUMB_CFLAGS)
 dnl ===========================================================================
 
 SAVE_CFLAGS="$CFLAGS"
+SAVE_LDFLAGS="$LDFLAGS"
 CFLAGS=""
+LDFLAGS=""
 AC_CHECK_LIB(m, floor,, AC_MSG_ERROR([math library not found]))
 M_LIBS="-lm"
 CFLAGS="$SAVE_CFLAGS"
+LDFLAGS="$SAVE_LDFLAGS"
 unset SAVE_CFLAGS
+unset SAVE_LDFLAGS
 AC_SUBST(M_LIBS)
 
 dnl ===========================================================================
@@ -378,7 +382,9 @@ AC_ARG_ENABLE([jpeg],
              [enable_jpeg=yes])
 if test "x$enable_jpeg" = "xyes"; then
        SAVE_CFLAGS="$CFLAGS"
+       SAVE_LDFLAGS="$LDFLAGS"
        CFLAGS=""
+       LDFLAGS=""
        AC_CHECK_LIB(jpeg, jpeg_destroy_decompress,
                     [enable_jpeg=yes],
                     [enable_jpeg=no])
@@ -387,7 +393,9 @@ if test "x$enable_jpeg" = "xyes"; then
                JPEG_LIBS='-ljpeg -lm -lz'
        fi
        CFLAGS="$SAVE_CFLAGS"
+       LDFLAGS="$SAVE_LDFLAGS"
        unset SAVE_CFLAGS
+       unset SAVE_LDFLAGS
 fi
 AC_SUBST(JPEG_LIBS)
 AM_CONDITIONAL(ENABLE_JPEG_TOOLS, test "x$enable_jpeg" = xyes)
@@ -422,7 +430,9 @@ AC_ARG_ENABLE([tiff],
              [enable_tiff=yes])
 if test x$enable_tiff = xyes ; then
        SAVE_CFLAGS="$CFLAGS"
+       SAVE_LDFLAGS="$LDFLAGS"
        CFLAGS=""
+       LDFLAGS=""
        AC_CHECK_LIB(tiff, TIFFWriteScanline,
                     [AC_CHECK_HEADER(tiffio.h,
                                      [enable_tiff=yes],
@@ -433,7 +443,9 @@ if test x$enable_tiff = xyes ; then
                TIFF_LIBS='-ltiff -lm -lz'
        fi
        CFLAGS="$SAVE_CFLAGS"
+       LDFLAGS="$SAVE_LDFLAGS"
        unset SAVE_CFLAGS
+       unset SAVE_LDFLAGS
 fi
 AC_SUBST(TIFF_LIBS)
 AM_CONDITIONAL(ENABLE_TIFF, test "x$enable_tiff" = xyes)