Fixes

• pkg-config files will take DESTDIR env var into account when selecting install destination (#3006, #3019)
• Changed filter to store the provided predicate by value (#3002, #3005)
  • This is done to avoid dangling-by-default behaviour when filter is used inside GENERATE_COPY/GENERATE_REF.

Improvements

• Escaping XML and JSON output is faster when the strings do not need escaping.
  • The improvement starts at about 3x throughput, up to 10x for long strings.
• Message macros (INFO, CAPTURE, WARN, SUCCEED, etc) are now thread safe.