[compiler-rt] Increase kDlsymAllocPoolSize to fix test failures

Increase kDlsymAllocPoolSize on the release branch as discussed on bug
51620, as an alternative to backporting
cb0e14ce and its dependencies.
The minimum size is 8192, as needed for the following test to pass:

  AddressSanitizer-i386-linux :: TestCases/Linux/long-object-path.cpp

Fixes #51620