Makefile: Fix building both static and shared library at the same time
Makefile: Fix building both static and shared library at the same time

Static library libdl.a must be build without -DSHARED flag for obvious
reason. So -DSHARED cannot be in global CFLAGS.

Define also two separate test targets: test.exe for shared library and
test-static.exe for static library.

dlfcn-win32/dlfcn-win32,dlfcn-win32/dlfcn-win32