Makefile: Fix build on MSYS2 and Cygwin

The host compiler on MSYS2 and Cygwin does not allow the -fPIC option,
issuing a warning that is treated as an error and stops the build.
Detect whether we're running under MSYS2 or Cygwin and avoid adding
-fPIC to prevent the error from happening.

Tested on Linux, MSYS2 and Cygwin.

Signed-off-by: Carles Cufi <carles.cufi@gmail.com>
[dwg: Added explicit empty CFLAGS for clarity]
Signed-off-by: David Gibson <david@gibson.dropbear.id.au>

Makefile

@@ -33,12 +33,16 @@ LIBDIR = $(PREFIX)/lib
 INCLUDEDIR = $(PREFIX)/include
 
 HOSTOS := $(shell uname -s | tr '[:upper:]' '[:lower:]' | \
-	    sed -e 's/\(cygwin\).*/cygwin/')
+	    sed -e 's/\(cygwin\|msys\).*/\1/')
 
 ifeq ($(HOSTOS),darwin)
 SHAREDLIB_EXT     = dylib
 SHAREDLIB_CFLAGS  = -fPIC
 SHAREDLIB_LDFLAGS = -fPIC -dynamiclib -Wl,-install_name -Wl,
+else ifeq ($(HOSTOS),$(filter $(HOSTOS),msys cygwin))
+SHAREDLIB_EXT     = so
+SHAREDLIB_CFLAGS  =
+SHAREDLIB_LDFLAGS = -shared -Wl,--version-script=$(LIBFDT_version) -Wl,-soname,
 else
 SHAREDLIB_EXT     = so
 SHAREDLIB_CFLAGS  = -fPIC