QRegularExpression: infrastructure for importing PCRE in 3rdparty/

QRegularExpression: infrastructure for importing PCRE in 3rdparty/

Added the necessary files for importing and compiling PCRE under
3rdparty/, including a small shell script to ease the import
and the update of PCRE from its dist tarball.

PCRE's config.h is used, but it is assumed that a global
  s/HAVE_CONFIG_H/PCRE_HAVE_CONFIG_H/g
was run on PCRE source files to avoid polluting QtCore
compilation with -DHAVE_CONFIG_H (the aforementioned shell script
performs this substitution; therefore, -DPCRE_HAVE_CONFIG_H
is added instead to the compiler's command line).

Change-Id: Ic0f23526ebf5f770aefdffc8f688e5816c28fd8c
Reviewed-by: Thiago Macieira <thiago.macieira@intel.com>
Reviewed-by: Oswald Buddenhagen <oswald.buddenhagen@nokia.com>