Add missing header to build config.

Bug: angleproject:6185
Change-Id: Ia3292935489e808bc53a6df3723d81355789b460
Reviewed-on: https://chromium-review.googlesource.com/c/angle/angle/+/3036588
Commit-Queue: Jeff Gilbert <jgilbert@mozilla.com>
Reviewed-by: Jamie Madill <jmadill@chromium.org>
Reviewed-by: Geoff Lang <geofflang@chromium.org>

src/compiler.gni

@@ -115,6 +115,7 @@ angle_translator_sources = [
   "src/compiler/translator/ValidateVaryingLocations.h",
   "src/compiler/translator/VariablePacker.cpp",
   "src/compiler/translator/VariablePacker.h",
+  "src/compiler/translator/VersionGLSL.h",
   "src/compiler/translator/blocklayout.cpp",
   "src/compiler/translator/glslang.h",
   "src/compiler/translator/glslang_lex_autogen.cpp",