runtime: allocate at desired address when race detector is on
Currently, on all supported platforms, the race detector (LLVM
TSAN) expects the Go heap is at 0xc000000000 - 0xe000000000.
Move the raceenabled condition first, so we always allocate
there.
This means on Linux/ARM64 when race detector is on we will
allocate to 0xc000000000 - 0xe000000000, instead of 0x4000000000.
The old address is meant for 39-bit VMA. But the race detector
only supports 48-bit VMA anyway. So this is fine.
Change-Id: I51ac8eff68297b37c8c651a93145cc94f83a939d
Reviewed-on: https://go-review.googlesource.com/c/go/+/266372
Trust: Cherry Zhang <cherryyz@google.com> Reviewed-by: Ian Lance Taylor <iant@golang.org>