Fix libEGL.so.1 issue with ANGLE build.

On Linux, ANGLE only builds a libEGL.so, while GLFW expects to find
libEGL.so.1. The fix is to force GLFW to load libEGL.so instead.

Bug: dawn:447
Change-Id: I4baa5b175a093b5b5d7a5c121085db3006c0e097
Reviewed-on: https://dawn-review.googlesource.com/c/dawn/+/39561
Reviewed-by: Corentin Wallez <cwallez@chromium.org>
Reviewed-by: Austin Eng <enga@chromium.org>
Commit-Queue: Stephen White <senorblanco@chromium.org>

third_party/gn/glfw/BUILD.gn

@@ -35,7 +35,12 @@ config("glfw_public") {
   }
 
   if (is_linux) {
-    defines = [ "_GLFW_X11" ]
+    # ANGLE builds only libEGL.so, so tell GLFW to load that instead of
+    # the default libEGL.so.1.
+    defines = [
+      "_GLFW_X11",
+      "_GLFW_EGL_LIBRARY=\"libEGL.so\"",
+    ]
   }
 }