Make vboot_reference build in MSVC command line environment.

This is a mostly NOOP change which modifies the source code
to compile cleanly in the MSVC command line build
environment.

A new makefile is introduced (msc/nmakefile) along with a
README.txt in the same directory explaining how to build
the code in the DOS window. As of this submission the build
is running in a 32 bit environment, the intention is to use
the same makefile for 64 bit builds in the future.

Enabling high compilation warnings level allowed to
identify a couple of bugs in the code which are being fixed.

Not all sources are being compiled in the MSVC environment,
only those in firmware/ and most of those in test/
subdirectories. The benchmark calculations require porting
of the timer facilities and are being postponed.

TEST

Built in DOS and linux environments. Ran unit tests in
linux environment.

Review URL: http://codereview.chromium.org/2809037
diff --git a/tests/sha_tests.c b/tests/sha_tests.c
index 2b75a03..65cbb46 100644
--- a/tests/sha_tests.c
+++ b/tests/sha_tests.c
@@ -78,6 +78,9 @@
   return success;
 }
 
+/* disable MSVC warnings on unused arguments */
+__pragma(warning (disable: 4100))
+
 int main(int argc, char* argv[]) {
   int success = 1;
   /* Initialize long_msg with 'a' x 1,000,000 */