When a header file is deleted, make will complain "No rule to make
target <old header file>". This often breaks incremental build
completely unnecessary.
This can be fixed by adding dummy rules for all header files like this:
<header file>:
gcc can create such rules by itself by using -MP in the generated make
dependency files, but that feature is not available for any other
compiler, so I opted not to use it, in favour of a solution that works
on all platforms.
This patch also contain a cosmetic fix for printing incremental build
information that was made somewhat less clear when the vardeps
functionality was introduced.
Bug: https://bugs.openjdk.java.net/browse/JDK-8072106
WebRev:
http://cr.openjdk.java.net/~ihse/JDK-8072106-make-dependency-targets-generation/webrev.01
/Magnus
