autoconf: Failure in Make Rules

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1 12.2 Failure in Make Rules
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1 Posix 2008 requires that `make' must invoke each command with the
1 equivalent of a `sh -e -c' subshell, which causes the subshell to exit
1 immediately if a subsidiary simple-command fails, although not all
1 `make' implementations have historically followed this rule.  For
1 example, the command `touch T; rm -f U' may attempt to remove `U' even
1 if the `touch' fails, although this is not permitted with Posix make.
1 One way to work around failures in simple commands is to reword them so
1 that they always succeed, e.g., `touch T || :; rm -f U'.  However, even
1 this approach can run into common bugs in BSD implementations of the
11 `-e' option of `sh' and `set' (⇒Limitations of Shell Builtins
 set.), so if you are worried about porting to buggy BSD shells it may
1 be simpler to migrate complicated `make' actions into separate scripts.
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