cgcc: add a configuration file for cgcc

The configuration file, ~/.cgccrc, allows a user to use perl syntax to set the $gcc_base_dir and $multiarch_dir variables, which would then suppress two compiler invocations. This can result in a marked performance boost on platforms for which the fork/exec costs are high (e.g. cygwin).

For example, on a multiarch system the file might look like:

    $ cat ~/.cgccrc
    $gcc_base_dir = "/usr/lib/gcc/x86_64-linux-gnu/4.8/";
    $multiarch_dir = "x86_64-linux-gnu";
    $

whereas for a non-multiarch system (e.g. cygwin):

    $ cat ~/.cgccrc
    $gcc_base_dir = "/usr/lib/gcc/x86_64-pc-cygwin/4.8.3/";
    $multiarch_dir = "";
    $

For me, on linux the difference in performance measured between 3-4% (e.g. 17.053s -> 16.379s to run sparse over the git sources), whereas on cygwin it measured about 20% (94.890s -> 76.207s).

---
 cgcc | 10 ++++++++--
 1 file changed, 8 insertions(+), 2 deletions(-)

index d7daa99..9d65438 100755
@@ -11,10 +11,16 @@ my $has_specs = 0;
 my $gendeps = 0;
 my $do_check = 0;
 my $do_compile = 1;
-my $gcc_base_dir;
-my $multiarch_dir;
+our $gcc_base_dir;
+our $multiarch_dir;
 my $verbose = 0;
 
+my $cgccrc_file = $ENV{'HOME'}."/.cgccrc" if $ENV{'HOME'};
+if (-e $cgccrc_file) {
+    do $cgccrc_file;
+    die $@ if $@;
+}
+
 while (@ARGV) {
     $_ = shift(@ARGV);
     # Look for a .c file.  We don't want to run the checker on .o or .so files

2.0.0