remove need for -Wno-narrowing

This is a default warning in GCC,
so it's kind of annoying if you just `g++ -c skcms.cc`.

PS1 works in GCC 7 and GCC 8, but is miscompiled by GCC 6.
PS2 seems fine in each.

(GCC 9 will also have __builtin_convertvector() like Clang.)

Change-Id: Ifcad3dd73fa30fca9663e7ebcc17701b4accd7e5
Reviewed-on: https://skia-review.googlesource.com/c/skcms/+/207915
Commit-Queue: Mike Klein <mtklein@google.com>
Auto-Submit: Mike Klein <mtklein@google.com>
Reviewed-by: Brian Osman <brianosman@google.com>
2 files changed