For unknown reasons, linking against CoreFoundation on macOS 10.10
sometimes causes mmap to ignore the hint address, which makes the Go
allocator incompatible with TSAN. Currently, the effect of this is to
run the allocator out of arena hints on the very first allocation,
causing a "too many address space collisions for -race mode" panic.

This CL skips the cgo tests that link against CoreFoundation in race
mode.

Updates #26475.
Updates #26513.

Change-Id: I52ec638c99acf5d4966e68ff0054f7679680dac6
Reviewed-on: https://go-review.googlesource.com/125304
Run-TryBot: Austin Clements <austin@google.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Ian Lance Taylor <iant@golang.org>
Reviewed-by: Keith Randall <khr@golang.org>