Merge branch 'ab/pcre-jit-fixes'

Merge branch 'ab/pcre-jit-fixes'

A few simplification and bugfixes to PCRE interface.

* ab/pcre-jit-fixes:
  grep: under --debug, show whether PCRE JIT is enabled
  grep: do not enter PCRE2_UTF mode on fixed matching
  grep: stess test PCRE v2 on invalid UTF-8 data
  grep: create a "is_fixed" member in "grep_pat"
  grep: consistently use "p->fixed" in compile_regexp()
  grep: stop using a custom JIT stack with PCRE v1
  grep: stop "using" a custom JIT stack with PCRE v2
  grep: remove overly paranoid BUG(...) code
  grep: use PCRE v2 for optimized fixed-string search
  grep: remove the kwset optimization
  grep: drop support for \0 in --fixed-strings <pattern>
  grep: make the behavior for NUL-byte in patterns sane
  grep tests: move binary pattern tests into their own file
  grep tests: move "grep binary" alongside the rest
  grep: inline the return value of a function call used only once
  t4210: skip more command-line encoding tests on MinGW
  grep: don't use PCRE2?_UTF8 with "log --encoding=<non-utf8>"
  log tests: test regex backends in "--encode=<enc>" tests