Enable skins2 automatically (rather than always)

It was rather confusing that XPM, Xinerama and Xext seemed absolutely
required even though only skins2 depends on them. Also the check for
libtar is now skipped if skins2 are disabled.

configure.ac

@@ -3580,29 +3580,10 @@ EXTEND_HELP_STRING([Interface plugins:])
 dnl
 dnl Skins2 module
 dnl
-AC_ARG_ENABLE(libtar,
-  [  --enable-libtar         libtar support for skins2 (default auto)])
-AS_IF([test "${enable_libtar}" != "no"], [
-  AC_CHECK_HEADERS(libtar.h, [
-    VLC_ADD_LIBS([skins2],[-ltar])
-  ])
-])
-
 AC_ARG_ENABLE(skins2,
-  [AS_HELP_STRING([--enable-skins2],[Skins2 interface module (default
-   enabled except on MacOSX and WinCE)])],, [
-  AS_IF([test "${SYS}" != "darwin" && test "${SYS}" != "mingwce"], [
-    enable_skins2="yes"
-  ], [
-    enable_skins2="no"
-  ])
-])
-AS_IF([test "${enable_skins2}" = "yes"], [
-  dnl freetype
-  AS_IF([test "${have_freetype}" != "yes"], [
-    AC_MSG_ERROR([Could not find FreeType (required for skins2)])
-  ])
-
+  [AS_HELP_STRING([--enable-skins2], [skins interface module (default auto)])])
+AS_IF([test "${enable_skins2}" != "no"], [
+  have_skins_deps="yes"
   AS_IF([test "${SYS}" = "mingw32"], [
     VLC_ADD_CPPFLAGS([skins2],[-U_OFF_T_ -U_off_t -Imodules/gui/skins2 -DWIN32_SKINS])
     VLC_ADD_CXXFLAGS([skins2],[-O2 -fno-rtti])
@@ -3614,19 +3595,38 @@ AS_IF([test "${enable_skins2}" = "yes"], [
     VLC_ADD_LIBS([skins2],[-Wl,-framework,Carbon])
 
   ], [
-    PKG_CHECK_MODULES([XPM], [xpm])
-    PKG_CHECK_MODULES([XINERAMA], [xinerama])
-    PKG_CHECK_MODULES([XEXT], [xext])
+    PKG_CHECK_MODULES([XPM], [xpm],, [have_skins_deps="no"])
+    PKG_CHECK_MODULES([XINERAMA], [xinerama],, [have_skins_deps="no"])
+    PKG_CHECK_MODULES([XEXT], [xext],, [have_skins_deps="no"])
     VLC_ADD_CPPFLAGS([skins2],[-Imodules/gui/skins2 ${X_CFLAGS} ${XEXT_CFLAGS} ${XPM_CFLAGS} -DX11_SKINS])
     VLC_ADD_CXXFLAGS([skins2],[-O2 -fno-rtti])
     VLC_ADD_LIBS([skins2],[${X_LIBS} ${X_PRE_LIBS} ${XEXT_LIBS} ${XPM_LIBS} ${XINERAMA_LIBS} -lX11])
 
   ])
+  AS_IF([test "${have_freetype}" != "yes"], [
+    have_skins_deps="no"
+  ])
+
+  AS_IF([test "${have_skins_deps}" = "no"], [
+    AS_IF([test "x${enable_skins2}" = "x"], [
+      AC_MSG_WARN([Skins2 interface disabled due to missing dependencies.])
+    ], [
+      AC_MSG_ERROR([Skins2 interface requires FreeType, libxpm, libxext and libxinerama])
+    ])
+  ])
   VLC_ADD_PLUGIN([skins2])
   ALIASES="${ALIASES} svlc"
 ])
 AM_CONDITIONAL(BUILD_SKINS, [test "${enable_skins2}" = "yes"])
 
+AC_ARG_ENABLE(libtar,
+  [  --enable-libtar         libtar support for skins2 (default auto)])
+AS_IF([test "${enable_skins2}" = "yes" && test "${enable_libtar}" != "no"], [
+  AC_CHECK_HEADERS(libtar.h, [
+    VLC_ADD_LIBS([skins2],[-ltar])
+  ])
+])
+
 dnl
 dnl Hildon UI
 dnl