configure: rely on libplacebo to find vulkan

It detects it on Android and we don't. Since the vulkan code is only used with libplacebo, we should only enable it when libplacebo can use it (and the user allows it).

This should fail to build on Android before it's rebased on top of a60ff650.

configure.ac

@@ -3249,6 +3249,13 @@ dnl
 
 EXTEND_HELP_STRING([Video plugins:])
 
+dnl
+dnl Vulkan
+dnl
+AC_ARG_ENABLE(vulkan,
+  [AS_HELP_STRING([--disable-vulkan],
+      [disable Vulkan support (default auto)])])
+
 dnl
 dnl  libplacebo support
 dnl
@@ -3260,8 +3267,21 @@ have_libplacebo_gl="no"
 AS_IF([test "$enable_libplacebo" != "no"], [
   PKG_CHECK_MODULES([LIBPLACEBO], [libplacebo >= 4.192], [
     AC_DEFINE([HAVE_LIBPLACEBO], [1], [Define to 1 if libplacebo is enabled.])
-    AC_CHECK_HEADER([libplacebo/vulkan.h], [VLC_ADD_PLUGIN([placebo_vk])])
-    AC_CHECK_HEADER([libplacebo/opengl.h], [
+
+    AS_IF([test "$enable_vulkan" != "no"], [
+      PLACEBO_HAS_VULKAN="$(${PKG_CONFIG} libplacebo --variable pl_has_vulkan)"
+      AS_IF([test "${PLACEBO_HAS_VULKAN}" = "1"], [
+        VLC_ADD_PLUGIN([placebo_vk])
+      ],[
+        AS_IF([test -n "${enable_vulkan}"], [
+          AC_MSG_ERROR([Vulkan enabled by libplacebo does not support.])
+        ])
+        enable_vulkan="no"
+      ])
+    ])
+
+    PLACEBO_HAS_OPENGL="$(${PKG_CONFIG} libplacebo --variable pl_has_opengl)"
+    AS_IF([test "${PLACEBO_HAS_OPENGL}" = "1"], [
         AC_DEFINE([HAVE_LIBPLACEBO_GL], [1], [Define to 1 if <libplacebo/opengl.h> is available.])
         VLC_ADD_PLUGIN([placebo_gl])
         VLC_ADD_PLUGIN([placebo_gles2])
@@ -3276,6 +3296,7 @@ AS_IF([test "$enable_libplacebo" != "no"], [
 ])
 AM_CONDITIONAL([HAVE_LIBPLACEBO], [test "$enable_libplacebo" != "no"])
 AM_CONDITIONAL([HAVE_LIBPLACEBO_GL], [test "$have_libplacebo_gl" = "yes"])
+AM_CONDITIONAL(HAVE_VULKAN, [test "$enable_vulkan" != "no"])
 
 dnl
 dnl  OpenGL
@@ -3321,24 +3342,6 @@ AM_CONDITIONAL([HAVE_GL], [test "${have_gl}" = "yes"])
 dnl OpenGL ES 2: depends on EGL 1.1
 PKG_HAVE_WITH_MODULES([GLES2], [glesv2], [enable GLES2 support (default auto)])
 
-dnl
-dnl Vulkan
-dnl
-AC_ARG_ENABLE(vulkan,
-  [AS_HELP_STRING([--disable-vulkan],
-      [disable Vulkan support (default auto)])])
-
-AS_IF([test "$enable_vulkan" != "no"], [
-  PKG_CHECK_MODULES([VULKAN], [vulkan >= 1.0.26], [
-  ], [
-    AS_IF([test -n "${enable_vulkan}"], [
-      AC_MSG_ERROR([${VULKAN_PKG_ERRORS}.])
-    ])
-    enable_vulkan="no"
-  ])
-])
-AM_CONDITIONAL(HAVE_VULKAN, [test "$enable_vulkan" != "no"])
-
 dnl
 dnl  Xlib
 dnl