os2: add port files for SDL2-2.0.4 from Andrey Vasilkin

only geniconv/iconv.h (was from LGPL libiconv) is replaced with a generic
minimal iconv.h based on public knowledge.

src/core/os2/geniconv/makefile

@@ -0,0 +1,37 @@
+#
+# Universal iconv implementation for OS/2.
+#
+# OpenWatcom makefile to build a library that uses kiconv.dll / iconv2.dll /
+# iconv.dll or OS/2 Uni*() API.
+#
+# Andrey Vasilkin, 2016.
+#
+
+LIBFILE = geniconv.lib
+
+all: $(LIBFILE) test.exe .symbolic
+
+CFLAGS = -I$(%WATCOM)/h/os2 -I$(%WATCOM)/h -I. -bt=os2 -q -d0 -w2
+
+SRCS = geniconv.c os2cp.c os2iconv.c
+SRCS+= sys2utf8.c
+
+OBJS = $(SRCS:.c=.obj)
+
+LIBS = libuls.lib libconv.lib $(LIBFILE)
+
+test.exe: $(LIBFILE) test.obj
+  wlink op quiet system os2v2 file test.obj lib {$(LIBS)} name $*
+
+$(LIBFILE): $(OBJS)
+  @if exist $@ rm $@
+  @for %f in ($(OBJS)) do wlib -q -b $* +%f
+
+.c.obj:
+    wcc386 $(CFLAGS) -fo=$^@ $<
+
+clean: .SYMBOLIC
+  @if exist *.obj rm *.obj
+  @if exist *.err rm *.err
+  @if exist $(LIBFILE) rm $(LIBFILE)
+  @if exist test.exe rm test.exe