RFR: JDK-8257547: Handle multiple prereqs on the same line in deps files

[Tim Bell]

On Tue, 1 Dec 2020 22:49:06 GMT, Erik Joelsson <erikj at openjdk.org> wrote:

> After fixing JDK-8256810 and starting to look into backporting it, I discovered more potential failing cases. Certain versions of GCC may sometimes output multiple prerequisite files on the same line. I think the easiest way to handle this new issue is to split such lines.
> 
> When splitting lines, we need to make sure to not just split on any space. Some compilers output the : of the rule with a leading space, and already split lines will have a space before the backslash.

As @magicus wrote - this is subtle but looks OKAY.

-------------

Marked as reviewed by tbell (Reviewer).

PR: https://git.openjdk.java.net/jdk/pull/1548