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To get round problems encountered when building in a DOS build
environment the generation of the .o file containing build identifier
strings is modified.
The problems encounterred were:
   1. DOS echo doesn't strip ' characters from the output text.
   2. git is not available from CMD.EXE so the BUILD_STRING value needs
      some other origin.

A BUILD_STRING value of "development build" is used for now.

MAKE_BUILD_STRINGS is used to customise build string generation in a DOS
environment. This variable is not defined in the UNIX build environment
make file helper, and so the existing build string generation behaviour
is retained in these build environments.

NOTE: This commit completes a cumulative series aimed at improving
      build portability across development environments.
      This enables the build to run on several new build environments,
      if the relevant tools are available.
      At this point the build is tested on Windows 7 Enterprise SP1,
      using CMD.EXE, Cygwin and Msys (MinGW),as well as a native
      Linux envionment".  The Windows platform builds used
      aarch64-none-elf-gcc.exe 4.9.1.  CMD.EXE and Msys used Gnu
      Make 3.81, cygwin used Gnu Make 4.1.

CAVEAT: The cert_create tool build is not tested on the Windows
        platforms (openssl-for-windows has a GPL license).

Change-Id: Iaa4fc89dbe2a9ebae87e2600c9eef10a6af30251