Expose surfaceless context extension strings

It seems like SwiftShader already supports surfaceless contexts properly in
eglMakeCurrent, so we might as well expose the extension strings.

Change-Id: I3c1b85296c46536df9a8bd754856d825307181d0
Reviewed-on: https://swiftshader-review.googlesource.com/17948
Tested-by: Alexis Hétu <sugoi@google.com>
Reviewed-by: Nicolas Capens <nicolascapens@google.com>

src/OpenGL/libEGL/libEGL.cpp

diff --git a/src/OpenGL/libEGL/libEGL.cpp b/src/OpenGL/libEGL/libEGL.cpp
index 5944efd..55ee224 100644
--- a/src/OpenGL/libEGL/libEGL.cpp
+++ b/src/OpenGL/libEGL/libEGL.cpp
@@ -203,6 +203,7 @@
 		               "EGL_KHR_gl_renderbuffer_image "
 		               "EGL_KHR_fence_sync "
 		               "EGL_KHR_image_base "
+		               "EGL_KHR_surfaceless_context "
 		               "EGL_ANDROID_framebuffer_target "
 		               "EGL_ANDROID_recordable");
 	case EGL_VENDOR: