pgsql: Add compat file for dynamically loading the functions that MinGW

Log Message:
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Add compat file for dynamically loading the functions that MinGW is missing
the imports for. Add RegisterWaitForSingleObject() to the list of such
functions, which should take care of the current buildfarm breakage.

Modified Files:
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    pgsql/src/backend/port/win32:
        Makefile (r1.10 -> r1.11)
        (http://developer.postgresql.org/cvsweb.cgi/pgsql/src/backend/port/win32/Makefile?r1=1.10&r2=1.11)

Added Files:
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    pgsql/src/backend/port/win32:
        mingwcompat.c (r1.1)

(http://developer.postgresql.org/cvsweb.cgi/pgsql/src/backend/port/win32/mingwcompat.c?rev=1.1&content-type=text/x-cvsweb-markup)