[Wconversion] Suppress warnings

Bug: 56258
Bug: 58162

Change-Id: I0c8b3b6daa6708120ca1d6f431df893d8e3a5ecf
Reviewed-on: https://fuchsia-review.googlesource.com/c/third_party/glslang/+/422897
Reviewed-by: Petr Hosek <phosek@google.com>
diff --git a/BUILD.gn b/BUILD.gn
index 7dbff8d..a14fa46 100644
--- a/BUILD.gn
+++ b/BUILD.gn
@@ -146,6 +146,7 @@
       "-Wno-unused-variable",
       "-Wno-unknown-warning-option",
       "-Wno-misleading-indentation",
+      "-Wno-conversion",
     ]
   }