Added Joachim's changes for MinGW.

src/interfaces/ecpg/pgtypeslib/dt_common.c

src/interfaces/ecpg/test/compat_informix/dec_test.pgc

src/interfaces/ecpg/test/expected/compat_informix-dec_test.c

src/interfaces/ecpg/test/expected/pgtypeslib-num_test.c

src/interfaces/ecpg/test/expected/pgtypeslib-num_test.stderr

src/interfaces/ecpg/test/expected/pgtypeslib-num_test2.c

src/interfaces/ecpg/test/expected/preproc-variable.c

src/interfaces/ecpg/test/expected/preproc-variable.stderr

src/interfaces/ecpg/test/expected/preproc-variable.stdout

src/interfaces/ecpg/test/pg_regress.sh

src/interfaces/ecpg/test/pgtypeslib/num_test.pgc

src/interfaces/ecpg/test/pgtypeslib/num_test2.pgc

src/interfaces/ecpg/test/preproc/variable.pgc