Enable output of variable names in ASan and MSan error reporting.

[JohanEngelen]

I've finally found what was the problem! Now the user will see the variable name that is overflown (close to the address read), e.g.:

=================================================================
==73095==ERROR: AddressSanitizer: stack-buffer-overflow on address 0x000101507f08 at pc 0x000100c7ece8 bp 0x000101507e70 sp 0x000101507e68
WRITE of size 4 at 0x000101507f08 thread T0
    #0 0x100c7ece4 in _D10asan_fiber3fooFPiZv asan_fiber.d:21
    #1 0x100c7ee1c in _D10asan_fiber6prefooFZv asan_fiber.d:31
    #2 0x100de8ecc in fiber_entryPoint+0x4c (asan_fiber.d.tmp:arm64+0x10016cecc)

Address 0x000101507f08 is located in stack of thread T0 at offset 72 in frame
    #0 0x100c7ed0c in _D10asan_fiber6prefooFZv asan_fiber.d:28

  This frame has 1 object(s):
    [32, 72) 'aiaiaiaiaiaiaiaiaiai' <== Memory access at offset 72 overflows this variable