String literals shouldn't be compared by pointer, especially if the
literal is declared in a header (so the two pointers can come from
different translation units, because the string literal might have a
different copy in each).

Use strcmp instead.

Bug: angleproject:4175
Change-Id: I6002ccb185f48928b67ce8a7b3508e427761a8c3
Reviewed-on: https://chromium-review.googlesource.com/c/angle/angle/+/1940568
Commit-Queue: Shahbaz Youssefi <syoussefi@chromium.org>
Reviewed-by: Jonah Ryan-Davis <jonahr@google.com>
Reviewed-by: Jamie Madill <jmadill@chromium.org>