Enable build on FreeBSD ports (includes DragonFly BSD)

Zstd has been introduced to FreeBSD ports
(http://www.freshports.org/archivers/zstd/) which DragonFly BSD also
uses.  FreeBSD and DragonFly use the install targets (albeit modified in
some cases) so they must be added to the associated Makefile filters.
diff --git a/Makefile b/Makefile
index 9f5e1eb..c7e7983 100644
--- a/Makefile
+++ b/Makefile
@@ -70,10 +70,10 @@
 	@echo Cleaning completed
 
 
-#------------------------------------------------------------------------
-#make install is validated only for Linux, OSX, kFreeBSD and Hurd targets
-#------------------------------------------------------------------------
-ifneq (,$(filter $(shell uname),Linux Darwin GNU/kFreeBSD GNU))
+#----------------------------------------------------------------------------------
+#make install is validated only for Linux, OSX, kFreeBSD, Hurd and some BSD targets
+#----------------------------------------------------------------------------------
+ifneq (,$(filter $(shell uname),Linux Darwin GNU/kFreeBSD GNU FreeBSD DragonFly))
 HOST_OS = POSIX
 install:
 	$(MAKE) -C $(ZSTDDIR) $@
diff --git a/lib/Makefile b/lib/Makefile
index 76731ab..6e0b014 100644
--- a/lib/Makefile
+++ b/lib/Makefile
@@ -98,8 +98,8 @@
 	@echo Cleaning library completed
 
 #------------------------------------------------------------------------
-#make install is validated only for Linux, OSX, kFreeBSD and Hurd targets
-ifneq (,$(filter $(shell uname),Linux Darwin GNU/kFreeBSD GNU))
+#make install is validated only for Linux, OSX, kFreeBSD, Hurd and some BSD targets
+ifneq (,$(filter $(shell uname),Linux Darwin GNU/kFreeBSD GNU FreeBSD DragonFly))
 
 libzstd.pc:
 libzstd.pc: libzstd.pc.in
diff --git a/programs/Makefile b/programs/Makefile
index a55268a..e9c99fd 100644
--- a/programs/Makefile
+++ b/programs/Makefile
@@ -154,10 +154,10 @@
 	@echo Cleaning completed
 
 
-#---------------------------------------------------------------------------------
-#make install is validated only for Linux, OSX, kFreeBSD, Hurd and OpenBSD targets
-#---------------------------------------------------------------------------------
-ifneq (,$(filter $(shell uname),Linux Darwin GNU/kFreeBSD GNU OpenBSD))
+#----------------------------------------------------------------------------------
+#make install is validated only for Linux, OSX, kFreeBSD, Hurd and some BSD targets
+#----------------------------------------------------------------------------------
+ifneq (,$(filter $(shell uname),Linux Darwin GNU/kFreeBSD GNU OpenBSD FreeBSD DragonFly))
 HOST_OS = POSIX
 install: zstd
 	@echo Installing binaries