Add swiftshader_vertex_routine_fuzzer

This fuzzer will add coverage of the following:
 - Swiftshader's GLSL to DX bytecode compiler
 - Swiftshader's DX bytecode to Reactor compiler
 - Reactor's Subzero backend
 - Swiftshader's vertex fixed function reactor code

The GLSL to DX bytecode compiler is using a TPoolAllocator,
a follow-up change will make it work better with ASan.

BUG=swiftshader:86

Change-Id: I504fcde7d8821296b3350ff84b28f9a705b178bf
Reviewed-on: https://chromium-review.googlesource.com/734904
Reviewed-by: Max Moroz <mmoroz@chromium.org>
Reviewed-by: Alexis Hétu <sugoi@chromium.org>
Commit-Queue: Corentin Wallez <cwallez@chromium.org>
Cr-Commit-Position: refs/heads/master@{#512334}

testing/libfuzzer/fuzzers/BUILD.gn

@@ -464,6 +464,13 @@ fuzzer_test("angle_translator_fuzzer") {
   libfuzzer_options = [ "max_len=1000" ]
 }
 
+fuzzer_test("swiftshader_vertex_routine_fuzzer") {
+  sources = []
+  deps = [
+    "//third_party/swiftshader:vertex_routine_fuzzer",
+  ]
+}
+
 fuzzer_test("sha1_fuzzer") {
   sources = [
     "sha1_fuzzer.cc",