Bug fixes:
- Fixed build error related to zlib on systems with older make versions
(regression in ccache 3.2.3).
- Made conversion-to-bool explicit to avoid build warnings (and potential
runtime errors) on legacy systems.
- Improved signal handling: Kill compiler on SIGTERM; wait for compiler to
exit before exiting; die appropriately.
- Minor fixes related to Windows support.
- The correct compression level is now used if compression is requested.
- Fixed a bug where cache cleanup could be run too early for caches larger
than 64 GiB on 32-bit systems.
e8ca6b7a62