build: Fix vulkan detection

Add missing 'test'

https://bugzilla.gnome.org/show_bug.cgi?id=776736

diff --git a/configure.ac b/configure.ac
index a521843eae5a0178cfabed7c95d62e4471eaaaa4..b70a89a82258e251882b80de5b4244d68670e128 100644 (file)
--- a/configure.ac
+++ b/configure.ac
@@ -1327,7 +1327,7 @@ if test "x$enable_vulkan" != "xno"; then
           [AC_CHECK_LIB([vulkan], [vkCreateInstance], [], [vulkan_error="Vulkan library not found"])],
           [vulkan_error="Vulkan header not found"])
       if test "x$vulkan_error" != "x"; then
-          if "x$enable_vulkan" = "xyes"; then
+          if test "x$enable_vulkan" = "xyes"; then
               AC_MSG_ERROR($vulkan_error)
           else
               AC_MSG_WARN($vulkan_error)