bug#13078: [PATCH] configure.ac: Cygwin build breaks when path to pkg-tool contains spaces

[Josh <josh@foxtail.org>]

Hi,

I tried building trunk under Cygwin for the first time a few days ago
(with the `--with-w32' switch, though I don't think that's relevant)
but the build failed because ./configure was finding a version of
pkg-config whose path contained whitespace.  This exposed some quoting
problems in configure.ac, fixed in the patch below.  Here's a snippet
of the session with some representative errors:

checking for cma_open in -lpthreads... no
./configure: line 10967: /cygdrive/c/Program: No such file or directory
*** Your version of pkg-config is too old. You need version 0.9.0 or newer.
*** See http://www.freedesktop.org/software/pkgconfig
checking for lgetfilecon in -lselinux... no
./configure: line 11304: /cygdrive/c/Program: No such file or directory
*** Your version of pkg-config is too old. You need version 0.9.0 or newer.
*** See http://www.freedesktop.org/software/pkgconfig
checking for gnutls_certificate_set_verify_function... no
[...]
checking for gpm.h... no
./configure: line 13122: /cygdrive/c/Program: No such file or directory
*** Your version of pkg-config is too old. You need version 0.9.0 or newer.
*** See http://www.freedesktop.org/software/pkgconfig
checking whether netdb declares h_errno... yes

In addition to the quoting problem, it appears that failure to open a
file is interpreted as having a version which is too old, which is
perhaps not ideal.  Here's the patch I applied locally that allowed me
to build successfully:

diff --git a/configure.ac b/configure.ac
index 085ca83..85c21e1 100644
--- a/configure.ac
+++ b/configure.ac
@@ -1189,10 +1189,10 @@ AC_DEFUN([PKG_CHECK_MODULES], [
       *** The pkg-config script could not be found. Make sure it is
in your path, or give the full path to pkg-config with the PKG_CONFIG
environment variable or --with-pkg-config-prog.  Or see
http://www.freedesktop.org/software/pkgconfig to get pkg-config.])],
[$4])
   else
      PKG_CONFIG_MIN_VERSION=0.9.0
-     if $PKG_CONFIG --atleast-pkgconfig-version $PKG_CONFIG_MIN_VERSION; then
+     if "$PKG_CONFIG" --atleast-pkgconfig-version $PKG_CONFIG_MIN_VERSION; then
         AC_MSG_CHECKING(for $2)

-        if $PKG_CONFIG --exists "$2" 2>&AS_MESSAGE_LOG_FD &&
+        if "$PKG_CONFIG" --exists "$2" 2>&AS_MESSAGE_LOG_FD &&
           $1_CFLAGS=`$PKG_CONFIG --cflags "$2" 2>&AS_MESSAGE_LOG_FD` &&
           $1_LIBS=`$PKG_CONFIG --libs "$2" 2>&AS_MESSAGE_LOG_FD`; then
            edit_cflags="
@@ -2027,7 +2027,7 @@ if test x"$pkg_check_gtk" = xyes; then
     AC_DEFINE(USE_GTK, 1, [Define to 1 if using GTK.])
     GTK_OBJ="gtkutil.o $GTK_OBJ"
     USE_X_TOOLKIT=none
-    if $PKG_CONFIG --atleast-version=2.10 gtk+-2.0; then
+    if "$PKG_CONFIG" --atleast-version=2.10 gtk+-2.0; then
       :
     else
       AC_MSG_WARN([[Your version of Gtk+ will have problems with