[rfe] dontcare for prerequisites

[Scott McPeak]

Attached is an enhancement I made to make-3.97.1 which adds a new
feature: when a preqrequisite's file name begins with a hyphen, it is
marked dontcare (and the hyphen stripped).  Then during rebuilding, if
that file doesn't exist and can't be remade, 'make' silently proceeds.

This is useful for dependencies in automatically-generated dependency
lists: if a header file gets renamed or deleted, 'make' should not be
bothered by the nonexistence of the file, as long as the dependency info
is regenerated "soon".

More detail is available on a page I put together describing my solution
to the autodependency problem (which I think is superior to the approach
given in the manual):

  http://www.cs.berkeley.edu/~smcpeak/autodepend/autodepend.html

Thanks,

-Scott

autodepend.patch
Description: Text document