Msys2 tweaks for pg_validatebackup corruption test
1. Tell Msys2 not to mangle the tablespace map parameter
2. If rmdir doesn't work, fall back to trying unlink on the entry in
pg_tblspc.
Discussion: https://postgr.es/m/
7330a7c7-ce5f-9769-39a1-
bdb0b32bb4a6@2ndQuadrant.com