common: s/_NT_ALTERNATE_SYMBOL_PATH/_NT_ALT_SYMBOL_PATH/
common: s/_NT_ALTERNATE_SYMBOL_PATH/_NT_ALT_SYMBOL_PATH/

There is inconsistency on MSDN regarding the exact spelling of this
environment variable, but _NT_ALT_SYMBOL_PATH seems to be the more
prevalent spelling.

jrfonseca/drmingw,jrfonseca/drmingw,jrfonseca/drmingw,jrfonseca/drmingw