Allow enabling and disabling GLX support, part II

After doing this for Meson in commit fc014fa1, let's do the same dance
for the Autotools build.

configure.ac

@@ -58,41 +58,71 @@ AC_CHECK_HEADER([KHR/khrplatform.h],
 # uintptr_t to a void *") by default.  Kill that.
 XORG_TESTSET_CFLAG(CWARNFLAGS, [-Wno-int-conversion])
 
-has_znow=yes
-
-case $host_os in
-    mingw*)
-        build_egl=no
-        build_glx=no
-        build_wgl=yes
-        # On windows, the DLL has to have all of its functions
-        # resolved at link time, so we have to link directly aginst
-        # opengl32.dll.  But that's the only GL provider, anyway.
-        EPOXY_LINK_LIBS="-lopengl32"
-
-        # Testing our built windows binaries requires that they be run
-        # under wine.  Yeah, we should be nice and autodetect, but
-        # there's lots of missing autodetection for the testsuite
-        # (like checking for EGL and GLX libs in non-windows.).
-        AC_SUBST([LOG_COMPILER], [wine])
-        ;;
-    darwin*)
-        build_egl=no
-        build_glx=no
-        build_wgl=no
-        build_apple=yes
-        has_znow=no
-        EPOXY_LINK_LIBS=""
-        ;;
-    *)
-        build_egl=yes
-        build_glx=yes
-        build_wgl=no
-        # On platforms with dlopen, we load everything dynamically and
-        # don't link against a specific window system or GL implementation.
-        EPOXY_LINK_LIBS=""
-        ;;
-esac
+AC_ARG_ENABLE([glx],
+              [AC_HELP_STRING([--enable-glx=@<:@auto,yes,no@:>@], [Enable GLX support @<:@default=auto@:>@])],
+              [enable_glx=$enableval],
+              [enable_glx=auto])
+
+# GLX can be used on different platforms, so we expose a
+# configure time switch to enable or disable it; in case
+# the "auto" default value is set, we only enable GLX
+# support on Linux and Unix
+AS_CASE([$enable_glx],
+  [auto], [
+    AS_CASE([$host_os],
+            [mingw*], [build_glx=no],
+            [darwin*], [build_glx=no],
+            [android*], [build_glx=no],
+            [build_glx=yes])
+  ],
+
+  [yes], [
+    build_glx=yes
+  ],
+
+  [no], [
+    build_glx=no
+  ],
+
+  [AC_MSG_ERROR([Invalid value "$enable_glx" for option "--enable-glx"])]
+])
+
+# The remaining platform specific API for GL/GLES are enabled
+# depending on the platform we're building for
+AS_CASE([$host_os],
+  [mingw*], [
+    build_egl=no
+    build_wgl=yes
+    has_znow=yes
+    # On windows, the DLL has to have all of its functions
+    # resolved at link time, so we have to link directly aginst
+    # opengl32.dll.  But that's the only GL provider, anyway.
+    EPOXY_LINK_LIBS="-lopengl32"
+
+    # Testing our built windows binaries requires that they be run
+    # under wine.  Yeah, we should be nice and autodetect, but
+    # there's lots of missing autodetection for the testsuite
+    # (like checking for EGL and GLX libs in non-windows.).
+    AC_SUBST([LOG_COMPILER], [wine])
+  ],
+
+  [darwin*], [
+    build_egl=no
+    build_wgl=no
+    build_apple=yes
+    has_znow=no
+    EPOXY_LINK_LIBS=""
+  ],
+
+  [
+    build_egl=yes
+    build_wgl=no
+    has_znow=yes
+    # On platforms with dlopen, we load everything dynamically and
+    # don't link against a specific window system or GL implementation.
+    EPOXY_LINK_LIBS=""
+   ]
+)
 
 AC_SUBST(EPOXY_LINK_LIBS)
 
@@ -161,9 +191,14 @@ AS_CASE(["$host"],
 
 AC_SUBST([VISIBILITY_CFLAGS])
 
-PKG_CHECK_MODULES(X11, [x11], [x11=yes], [x11=no])
-if test x$x11 = xno -a x$build_glx = xyes; then
-    AC_MSG_ERROR([libX11 headers (libx11-dev) required to build with GLX support])
+if test x$build_glx = xyes; then
+  PKG_CHECK_MODULES(X11, [x11], [x11=yes], [x11=no])
+  if test x$x11 = xno -a x$build_glx = xyes; then
+      AC_MSG_ERROR([libX11 headers (libx11-dev) required to build with GLX support])
+  fi
+  AC_DEFINE(ENABLE_GLX, [1], [Whether GLX support is enabled])
+else
+  x11=no
 fi
 
 AM_CONDITIONAL(HAVE_X11, test x$x11 = xyes)

test/Makefile.am

@@ -72,8 +72,11 @@ check_PROGRAMS = $(TESTS)
 
 if BUILD_EGL
 EGL_TESTS = \
+	$()
+
+if HAVE_X11
+EGL_TESTS += \
 	egl_has_extension_nocontext \
-	egl_gl \
 	egl_gles2_without_glx \
 	$()
 
@@ -83,6 +86,7 @@ endif
 
 EGL_UTIL_LIB = libegl_common.la
 endif
+endif
 
 if BUILD_GLX
 if HAS_ZNOW
@@ -93,6 +97,7 @@ if BUILD_EGL
 if BUILD_GLX
 if !BUILD_APPLE
 EGL_AND_GLX_TESTS = \
+	egl_gl \
 	egl_and_glx_different_pointers_egl_glx \
 	egl_and_glx_different_pointers_egl \
 	egl_and_glx_different_pointers_glx \