BUILD: Makefile: shorten default settings declaration

By using a "default_opts" function we can enumerate at once all the
settings we want to enable by default for each platform instead of
individually assigning each variable. Doing this removed 46 lines
in the makefile.
diff --git a/Makefile b/Makefile
index 561b9cc..f2c81bc 100644
--- a/Makefile
+++ b/Makefile
@@ -287,6 +287,7 @@
 # options string. They may be set to any value, but are historically set to
 # "implicit" which eases debugging. You should not have to change anything
 # there unless you're adding support for a new platform.
+default_opts = $(foreach name,$(1),$(eval $(name)=implicit))
 
 # poll() is always supported, unless explicitly disabled by passing USE_POLL=""
 # on the make command line.
@@ -297,137 +298,90 @@
 
 ifeq ($(TARGET),generic)
   # generic system target has nothing specific
-  USE_POLL   = implicit
-  USE_TPROXY = implicit
+  $(call default_opts,USE_POLL USE_TPROXY)
 else
 ifeq ($(TARGET),haiku)
   # For Haiku
   TARGET_LDFLAGS = -lnetwork
-  USE_POLL = implicit
-  USE_TPROXY = implicit
+  $(call default_opts,USE_POLL USE_TPROXY)
 else
 ifeq ($(TARGET),linux22)
   # This is for Linux 2.2
-  USE_POLL        = implicit
-  USE_TPROXY      = implicit
-  USE_LIBCRYPT    = implicit
-  USE_DL          = implicit
-  USE_RT          = implicit
+  $(call default_opts, \
+    USE_POLL USE_TPROXY USE_LIBCRYPT USE_DL USE_RT)
 else
 ifeq ($(TARGET),linux24)
   # This is for standard Linux 2.4 with netfilter but without epoll()
-  USE_NETFILTER   = implicit
-  USE_POLL        = implicit
-  USE_TPROXY      = implicit
-  USE_CRYPT_H     = implicit
-  USE_LIBCRYPT    = implicit
-  USE_DL          = implicit
-  USE_RT          = implicit
+  $(call default_opts, \
+    USE_POLL USE_TPROXY USE_LIBCRYPT USE_DL USE_RT USE_CRYPT_H USE_NETFILTER)
 else
 ifeq ($(TARGET),linux24e)
   # This is for enhanced Linux 2.4 with netfilter and epoll() patch > 0.21
-  USE_NETFILTER   = implicit
-  USE_POLL        = implicit
-  USE_EPOLL       = implicit
-  USE_MY_EPOLL    = implicit
-  USE_TPROXY      = implicit
-  USE_CRYPT_H     = implicit
-  USE_LIBCRYPT    = implicit
-  USE_DL          = implicit
-  USE_RT          = implicit
+  $(call default_opts, \
+    USE_POLL USE_TPROXY USE_LIBCRYPT USE_DL USE_RT USE_CRYPT_H USE_NETFILTER  \
+    USE_EPOLL USE_MY_EPOLL)
 else
 ifeq ($(TARGET),linux26)
   # This is for standard Linux 2.6 with netfilter and standard epoll()
-  USE_NETFILTER   = implicit
-  USE_POLL        = implicit
-  USE_EPOLL       = implicit
-  USE_TPROXY      = implicit
-  USE_CRYPT_H     = implicit
-  USE_LIBCRYPT    = implicit
-  USE_FUTEX       = implicit
-  USE_DL          = implicit
-  USE_RT          = implicit
+  $(call default_opts, \
+    USE_POLL USE_TPROXY USE_LIBCRYPT USE_DL USE_RT USE_CRYPT_H USE_NETFILTER  \
+    USE_EPOLL USE_FUTEX)
 else
 ifeq ($(TARGET),linux2628)
   # This is for standard Linux >= 2.6.28 with netfilter, epoll, tproxy and splice
-  USE_NETFILTER   = implicit
-  USE_POLL        = implicit
-  USE_EPOLL       = implicit
-  USE_TPROXY      = implicit
-  USE_CRYPT_H     = implicit
-  USE_LIBCRYPT    = implicit
-  USE_LINUX_SPLICE= implicit
-  USE_LINUX_TPROXY= implicit
-  USE_ACCEPT4     = implicit
-  USE_FUTEX       = implicit
-  USE_CPU_AFFINITY= implicit
-  ASSUME_SPLICE_WORKS= implicit
-  USE_DL          = implicit
-  USE_RT          = implicit
-  USE_THREAD      = implicit
+  $(call default_opts, \
+    USE_POLL USE_TPROXY USE_LIBCRYPT USE_DL USE_RT USE_CRYPT_H USE_NETFILTER  \
+    USE_CPU_AFFINITY USE_THREAD USE_EPOLL USE_FUTEX USE_LINUX_TPROXY          \
+    USE_ACCEPT4 USE_LINUX_SPLICE ASSUME_SPLICE_WORKS)
 else
 ifeq ($(TARGET),solaris)
   # This is for Solaris 8
   # We also enable getaddrinfo() which works since solaris 8.
-  USE_POLL       = implicit
+  $(call default_opts, \
+    USE_POLL USE_TPROXY USE_LIBCRYPT USE_CRYPT_H USE_GETADDRINFO USE_THREAD)
   TARGET_CFLAGS  = -fomit-frame-pointer -DFD_SETSIZE=65536 -D_REENTRANT -D_XOPEN_SOURCE=500 -D__EXTENSIONS__
   TARGET_LDFLAGS = -lnsl -lsocket
-  USE_TPROXY     = implicit
-  USE_LIBCRYPT    = implicit
-  USE_CRYPT_H     = implicit
-  USE_GETADDRINFO = implicit
-  USE_THREAD      = implicit
 else
 ifeq ($(TARGET),freebsd)
   # This is for FreeBSD
-  USE_POLL       = implicit
-  USE_KQUEUE     = implicit
-  USE_TPROXY     = implicit
-  USE_LIBCRYPT   = implicit
-  USE_THREAD     = implicit
-  USE_CPU_AFFINITY= implicit
-  USE_CLOSEFROM  = implicit
+  $(call default_opts, \
+    USE_POLL USE_TPROXY USE_LIBCRYPT USE_THREAD USE_CPU_AFFINITY USE_KQUEUE   \
+    USE_CLOSEFROM)
 else
 ifeq ($(TARGET),osx)
   # This is for Mac OS/X
-  USE_POLL       = implicit
-  USE_KQUEUE     = implicit
-  USE_TPROXY     = implicit
+  $(call default_opts, \
+    USE_POLL USE_TPROXY USE_KQUEUE)
   EXPORT_SYMBOL  = -export_dynamic
 else
 ifeq ($(TARGET),openbsd)
   # This is for OpenBSD >= 5.7
-  USE_POLL       = implicit
-  USE_KQUEUE     = implicit
-  USE_TPROXY     = implicit
-  USE_ACCEPT4    = implicit
-  USE_THREAD     = implicit
+  $(call default_opts, \
+    USE_POLL USE_TPROXY USE_THREAD USE_KQUEUE USE_ACCEPT4)
 else
 ifeq ($(TARGET),netbsd)
   # This is for NetBSD
-  USE_POLL       = implicit
-  USE_KQUEUE     = implicit
-  USE_TPROXY     = implicit
+  $(call default_opts, \
+    USE_POLL USE_TPROXY USE_KQUEUE)
 else
 ifeq ($(TARGET),aix51)
   # This is for AIX 5.1
-  USE_POLL        = implicit
-  USE_LIBCRYPT    = implicit
+  $(call default_opts, \
+    USE_POLL USE_LIBCRYPT)
   TARGET_CFLAGS   = -Dss_family=__ss_family
   DEBUG_CFLAGS    =
 else
 ifeq ($(TARGET),aix52)
   # This is for AIX 5.2 and later
-  USE_POLL        = implicit
-  USE_LIBCRYPT    = implicit
+  $(call default_opts, \
+    USE_POLL USE_LIBCRYPT)
   TARGET_CFLAGS   = -D_MSGQSUPPORT
   DEBUG_CFLAGS    =
 else
 ifeq ($(TARGET),cygwin)
   # This is for Cygwin
   # Cygwin adds IPv6 support only in version 1.7 (in beta right now). 
-  USE_POLL   = implicit
-  USE_TPROXY = implicit
+  $(call default_opts,USE_POLL USE_TPROXY)
   TARGET_CFLAGS  = $(if $(filter 1.5.%, $(shell uname -r)), -DUSE_IPV6 -DAF_INET6=23 -DINET6_ADDRSTRLEN=46, )
 endif # cygwin
 endif # aix52