Merge branch 'ab/grep-pcre2-allocfix'
Updates to memory allocation code around the use of pcre2 library.
* ab/grep-pcre2-allocfix:
grep/pcre2: move definitions of pcre2_{malloc,free}
grep/pcre2: move back to thread-only PCREv2 structures
grep/pcre2: actually make pcre2 use custom allocator
grep/pcre2: use pcre2_maketables_free() function
grep/pcre2: use compile-time PCREv2 version test
grep/pcre2: add GREP_PCRE2_DEBUG_MALLOC debug mode
grep/pcre2: prepare to add debugging to pcre2_malloc()
grep/pcre2: correct reference to grep_init() in comment
grep/pcre2: drop needless assignment to NULL
grep/pcre2: drop needless assignment + assert() on opt->pcre2