Generate cordtest and de executable files in GC base folder

Generate cordtest and de executable files in GC base folder

This is to match the behavior of Automake- and CMake-based scripts.

* BCC_MAKEFILE (all, cord\de.exe): Rename cord\de.exe to de.exe.
* NT_MAKEFILE (all, cord\de.exe): Likewise.
* doc/README.win32: Likewise.
* Makefile.direct (cord/cordtest, clean, check): Rename cord/cordtest to
cordtest.
* SMakefile.amiga (all, clean, test, cord/cordtest): Likewise.
* Makefile.direct (cord/de): Rename cord/de to de$(EXEEXT); add cord/de
rule depending on de$(EXEEXT).
* Makefile.direct (clean): Rename cord/de to de.
* doc/README.cords: Likewise.
* OS2_MAKEFILE (all, cord\cordtest.exe): Rename cord\cordtest.exe to
cordtest.exe.