[DFSan] Fix flakey release_shadow_space.c accounting for Origin chains.

Test sometimes fails on buildbot (after two non-Origins executions):

/usr/bin/ld: warning: Cannot export local symbol 'dfsan_flush'
RSS at start: 4620, after mmap: 107020, after mmap+set label: 209424, after fixed map: 4624, after another mmap+set label: 209424, after munmap: 4624
/usr/bin/ld: warning: Cannot export local symbol 'dfsan_flush'
RSS at start: 4620, after mmap: 107020, after mmap+set label: 209424, after fixed map: 4624, after another mmap+set label: 209424, after munmap: 4624
/usr/bin/ld: warning: Cannot export local symbol 'dfsan_flush'
RSS at start: 4620, after mmap: 107020, after mmap+set label: 317992, after fixed map: 10792, after another mmap+set label: 317992, after munmap: 10792
release_shadow_space.c.tmp: /b/sanitizer-x86_64-linux/build/llvm-project/compiler-rt/test/dfsan/release_shadow_space.c:91: int main(int, char **): Assertion `after_fixed_mmap <= before + delta' failed.

Reviewed By: vitalybuka

Differential Revision: https://reviews.llvm.org/D111522