libgui: export EGL headers.

Many libgui headers use these headers so not exporting
these breaks BOARD_VNDK_VERSION=current builds.

Test: headers resolved with BOARD_VNDK_VERSION=current
Change-Id: I085faeda4f8ad8a07d91e81222b8031a0dd1858a
diff --git a/libs/gui/Android.bp b/libs/gui/Android.bp
index 4f8d374..497bd19 100644
--- a/libs/gui/Android.bp
+++ b/libs/gui/Android.bp
@@ -130,8 +130,9 @@
 
     export_shared_lib_headers: [
         "libbinder",
-        "libui",
+        "libEGL",
         "libnativewindow",
+        "libui",
         "android.hidl.token@1.0-utils",
         "android.hardware.graphics.bufferqueue@1.0",
     ],