Customize glslang.y to GLSLANG_ANGLE

glslang.y is specialized to remove what is not supported or won't be
supported by ANGLE.

This change shaves about 125KB off of ANGLE's binary size with minor
improvement to the cost of SetupBuiltinSymbolTable.

Signed-off-by: Shahbaz Youssefi <ShabbyX@gmail.com>

BUILD.gn

@@ -130,7 +130,7 @@ template("glslang_sources_common") {
       "glslang/MachineIndependent/attribute.cpp",
       "glslang/MachineIndependent/attribute.h",
       "glslang/MachineIndependent/gl_types.h",
-      "glslang/MachineIndependent/glslang_tab.cpp",
+      "glslang/MachineIndependent/glslang_angle_tab.cpp.h",
       "glslang/MachineIndependent/glslang_tab.cpp.h",
       "glslang/MachineIndependent/intermOut.cpp",
       "glslang/MachineIndependent/iomapper.cpp",
@@ -181,6 +181,18 @@ template("glslang_sources_common") {
     }
 
     defines = []
+    if (invoker.is_angle) {
+      sources += [
+        "glslang/MachineIndependent/glslang_angle_tab.cpp",
+      ]
+      defines += [ "GLSLANG_ANGLE" ]
+    }
+    else {
+      sources += [
+        "glslang/MachineIndependent/glslang_tab.cpp",
+      ]
+    }
+
     if (invoker.enable_opt) {
       sources += [ "SPIRV/SpvTools.cpp" ]
       defines += [ "ENABLE_OPT=1" ]