mingw32-pcre: Add package

Buildjob is at http://mingwgitdevenv.cloudapp.net/job/mingwGitDevEnv-build-packages/150.
Unfortunately it did not finish.
Looks like the package mingw32-gcc-g++ was not installed although it is referenced in https://github.com/sschuberth/mingwGitDevEnv/blob/master/installer/installer.iss#L102. Thats strange.

With this package and the below patch we can build git with pcre support.
```diff
From 546b4b4332e52dedfb020c4b6b45df7d0538f31c Mon Sep 17 00:00:00 2001
From: Thomas Braun <thomas.braun@byte-physics.de>
Date: Wed, 11 Jun 2014 23:14:23 +0200
Subject: [PATCH] Add PCRE as build dependency

Signed-off-by: Thomas Braun <thomas.braun@byte-physics.de>

diff --git a/config.mak.uname b/config.mak.uname
index 82b8dff..bc6836a 100644
--- a/config.mak.uname
+++ b/config.mak.uname
@@ -530,6 +530,7 @@ ifneq (,$(wildcard ../THIS_IS_MSYSGIT))
        INTERNAL_QSORT = YesPlease
        HAVE_LIBCHARSET_H = YesPlease
        NO_GETTEXT = YesPlease
+       LIBPCRE = YesPlease
 else
        NO_CURL = YesPlease
 endif
--
1.9.4.msysgit.0
```
The tests in t7810-grep.sh are now all executed and pass.