ast: intrinsic spelling matches the spec

Update the comments around the stream output method for ast::Intrinsic.

Change-Id: I06a3082927c83eb9172357c34a0587aac5f80465
Reviewed-on: https://dawn-review.googlesource.com/c/tint/+/32360
Reviewed-by: dan sinclair <dsinclair@chromium.org>
Commit-Queue: dan sinclair <dsinclair@chromium.org>

src/ast/intrinsic.cc

@@ -18,6 +18,8 @@ namespace tint {
 namespace ast {
 
 std::ostream& operator<<(std::ostream& out, Intrinsic i) {
+  /// The emitted name matches the spelling in the WGSL spec.
+  /// including case.
   switch (i) {
     case Intrinsic::kAbs:
       out << "abs";

src/ast/intrinsic.h

@@ -93,6 +93,8 @@ enum class Intrinsic {
   kTrunc
 };
 
+/// Emits the name of the intrinsic function. The spelling,
+/// including case, matches the name in the WGSL spec.
 std::ostream& operator<<(std::ostream& out, Intrinsic i);
 
 namespace intrinsic {