Add __attribute__((__format__(printf))) to functions that take a printf-compatible format string (when building using GCC or Clang), so that format string mistakes can be detected statically.
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Change: 185021
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* New nmake file w3i6pc.nmk.
* New stack scanner ssw3i6pc.c supplies missing jump buffer definition.
* Some platform tests change from defined(MPS_PF_W3I6MV) to defined(MPS_OS_w3) && defined(MPS_ARCH_I6).
* Make reasonable changes to the source code to avoid warnings from Pelles C:
** Ensure that printf formats are consistent with arguments by using PRIuLONGEST and casting to ulongest_t.
** Use size_t for loop variables that index into arrays.
** Suppress "Consider changing type to 'size_t' for loop variable" warnings for the MPS core.
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Change: 184996
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