Import bmake-20230622

Relevant/interesting changes:

o optimize string matching for ':M' and ':N'
o warn about malformed patterns in ':M', ':N' and '.if make(...)'
o allow guards to be targets as well as variables
The guard targets may include variable references like
${.PARSEDIR:tA}/${.PARSEFILE}
o optimization for makefiles protected from multiple-inclusion
skip even opening the file after first include.
o var.c: do not allow delete of readOnly variable
o parse.c: .break takes no args