Fixes to shared makefiles
Ben Avison authored
Detail:
  The change which permitted top-level makefiles to include only CApp,
  CModule etc accidentally broke makefiles which included HostTools (StdTools
  got included instead and overwrote the HostTools settings). Amazingly, we
  seem to have got away with this so far - but fixed now. Also, brought the
  GNUmakefiles versions in line with updates to the amu Makefiles in this
  and other respects.
Admin:
  Tested in a RISC OS ROM build, and for building cross-compiling versions
  of the tools.

Version 5.21. Tagged as 'BuildSys-5_21'
70323f40