Add gdb (7.12.1) package

This adds the GNU debugger as a package. Compilation takes a while on
this one as it's fairly large and complex.

Tested as working properly on Samsung XE50013-K01US.

packages/gdb.rb

+require 'package'
+
+class Gdb < Package
+  version '7.12.1.' 
+  source_url 'https://ftp.gnu.org/gnu/gdb/gdb-7.12.1.tar.xz'
+  source_sha1 'ef77c5345d6f9fdcdf7a5d8503301242b701936e'
+
+  depends_on "buildessential"
+  depends_on "ncurses"
+  depends_on "texinfo"
+
+  def self.build
+    system "./configure", "--prefix=/usr/local"
+    system "make"
+  end
+
+  def self.install
+    system "make", "DESTDIR=#{CREW_DEST_DIR}", "install"
+  end
+end