[ccache] ccache direct mode

[tridge at samba.org]

Hi Joel,

 > The basic idea of how to achieve this is finding out which files were
 > included by the preprocessor and then storing the hash sums of those
 > files in a file associated with the input file and compiler arguments.

How dependent is this on the compiler? Is the format of the include
file names on different compilers (eg. sun compiler) consistent enough
for this to be reliable?

Also, does the hashtable used for included_files preserve the
ordering? (the order of includes is also vital). Or do you rely on the
hash of the file that does the #include changing for that?

Cheers, Tridge