[tint][glsl] Put GLSL validation behind a build flag.

This can be disabled if the outer project does not have glslang.

Change-Id: Ia0dad6e1ef0b9936bf035f94c9a04e33f62db6ce
Reviewed-on: https://dawn-review.googlesource.com/c/dawn/+/155721
Reviewed-by: Corentin Wallez <cwallez@chromium.org>
Kokoro: Kokoro <noreply+kokoro@google.com>
Commit-Queue: Ben Clayton <bclayton@google.com>
diff --git a/src/tint/CMakeLists.txt b/src/tint/CMakeLists.txt
index 7a0add5..d674fde 100644
--- a/src/tint/CMakeLists.txt
+++ b/src/tint/CMakeLists.txt
@@ -37,6 +37,7 @@
   target_compile_definitions(${TARGET} PUBLIC -DTINT_BUILD_SPV_READER=$<BOOL:${TINT_BUILD_SPV_READER}>)
   target_compile_definitions(${TARGET} PUBLIC -DTINT_BUILD_WGSL_READER=$<BOOL:${TINT_BUILD_WGSL_READER}>)
   target_compile_definitions(${TARGET} PUBLIC -DTINT_BUILD_GLSL_WRITER=$<BOOL:${TINT_BUILD_GLSL_WRITER}>)
+  target_compile_definitions(${TARGET} PUBLIC -DTINT_BUILD_GLSL_VALIDATOR=$<BOOL:${TINT_BUILD_GLSL_VALIDATOR}>)
   target_compile_definitions(${TARGET} PUBLIC -DTINT_BUILD_HLSL_WRITER=$<BOOL:${TINT_BUILD_HLSL_WRITER}>)
   target_compile_definitions(${TARGET} PUBLIC -DTINT_BUILD_MSL_WRITER=$<BOOL:${TINT_BUILD_MSL_WRITER}>)
   target_compile_definitions(${TARGET} PUBLIC -DTINT_BUILD_SPV_WRITER=$<BOOL:${TINT_BUILD_SPV_WRITER}>)