BUILD: makefile: work around another bug in make 3.80

GNU make 3.80 has an issue with calls to functions inside an if block,
which is just what we recently introduced to simplify the targets
declaration. The fix is easy, it simply consists in assigning the
command to a variable inside the if block and evaluating this command
after the block. This also makes the code slightly more readable so we
can keep compatibility with 3.80 for now.

No backport is needed.

Makefile

@@ -298,44 +298,44 @@ USE_POLL   = default
 
 # generic system target has nothing specific
 ifeq ($(TARGET),generic)
-  $(call default_opts,USE_POLL USE_TPROXY)
+  set_target_defaults = $(call default_opts,USE_POLL USE_TPROXY)
 endif
 
 # Haiku
 ifeq ($(TARGET),haiku)
   TARGET_LDFLAGS = -lnetwork
-  $(call default_opts,USE_POLL USE_TPROXY)
+  set_target_defaults = $(call default_opts,USE_POLL USE_TPROXY)
 endif
 
 # Linux 2.2
 ifeq ($(TARGET),linux22)
-  $(call default_opts, \
+  set_target_defaults = $(call default_opts, \
     USE_POLL USE_TPROXY USE_LIBCRYPT USE_DL USE_RT)
 endif
 
 # Standard Linux 2.4 with netfilter but without epoll()
 ifeq ($(TARGET),linux24)
-  $(call default_opts, \
+  set_target_defaults = $(call default_opts, \
     USE_POLL USE_TPROXY USE_LIBCRYPT USE_DL USE_RT USE_CRYPT_H USE_NETFILTER)
 endif
 
 # Enhanced Linux 2.4 with netfilter and epoll() patch > 0.21
 ifeq ($(TARGET),linux24e)
-  $(call default_opts, \
+  set_target_defaults = $(call default_opts, \
     USE_POLL USE_TPROXY USE_LIBCRYPT USE_DL USE_RT USE_CRYPT_H USE_NETFILTER  \
     USE_EPOLL USE_MY_EPOLL)
 endif
 
 # Standard Linux 2.6 with netfilter and standard epoll()
 ifeq ($(TARGET),linux26)
-  $(call default_opts, \
+  set_target_defaults = $(call default_opts, \
     USE_POLL USE_TPROXY USE_LIBCRYPT USE_DL USE_RT USE_CRYPT_H USE_NETFILTER  \
     USE_EPOLL USE_FUTEX)
 endif
 
 # Standard Linux >= 2.6.28 with netfilter, epoll, tproxy and splice
 ifeq ($(TARGET),linux2628)
-  $(call default_opts, \
+  set_target_defaults = $(call default_opts, \
     USE_POLL USE_TPROXY USE_LIBCRYPT USE_DL USE_RT USE_CRYPT_H USE_NETFILTER  \
     USE_CPU_AFFINITY USE_THREAD USE_EPOLL USE_FUTEX USE_LINUX_TPROXY          \
     USE_ACCEPT4 USE_LINUX_SPLICE ASSUME_SPLICE_WORKS)
@@ -344,7 +344,7 @@ endif
 # Solaris 8 and above
 ifeq ($(TARGET),solaris)
   # We also enable getaddrinfo() which works since solaris 8.
-  $(call default_opts, \
+  set_target_defaults = $(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
@@ -352,33 +352,33 @@ endif
 
 # FreeBSD 5 and above
 ifeq ($(TARGET),freebsd)
-  $(call default_opts, \
+  set_target_defaults = $(call default_opts, \
     USE_POLL USE_TPROXY USE_LIBCRYPT USE_THREAD USE_CPU_AFFINITY USE_KQUEUE   \
     USE_CLOSEFROM)
 endif
 
 # Mac OS/X
 ifeq ($(TARGET),osx)
-  $(call default_opts, \
+  set_target_defaults = $(call default_opts, \
     USE_POLL USE_TPROXY USE_KQUEUE)
   EXPORT_SYMBOL  = -export_dynamic
 endif
 
 # OpenBSD 5.7 and above
 ifeq ($(TARGET),openbsd)
-  $(call default_opts, \
+  set_target_defaults = $(call default_opts, \
     USE_POLL USE_TPROXY USE_THREAD USE_KQUEUE USE_ACCEPT4)
 endif
 
 # NetBSD
 ifeq ($(TARGET),netbsd)
-  $(call default_opts, \
+  set_target_defaults = $(call default_opts, \
     USE_POLL USE_TPROXY USE_KQUEUE)
 endif
 
 # AIX 5.1 only
 ifeq ($(TARGET),aix51)
-  $(call default_opts, \
+  set_target_defaults = $(call default_opts, \
     USE_POLL USE_LIBCRYPT)
   TARGET_CFLAGS   = -Dss_family=__ss_family
   DEBUG_CFLAGS    =
@@ -386,7 +386,7 @@ endif
 
 # AIX 5.2 and above
 ifeq ($(TARGET),aix52)
-  $(call default_opts, \
+  set_target_defaults = $(call default_opts, \
     USE_POLL USE_LIBCRYPT)
   TARGET_CFLAGS   = -D_MSGQSUPPORT
   DEBUG_CFLAGS    =
@@ -394,11 +394,14 @@ endif
 
 # Cygwin
 ifeq ($(TARGET),cygwin)
-  $(call default_opts,USE_POLL USE_TPROXY)
+  set_target_defaults = $(call default_opts,USE_POLL USE_TPROXY)
   # Cygwin adds IPv6 support only in version 1.7 (in beta right now). 
   TARGET_CFLAGS  = $(if $(filter 1.5.%, $(shell uname -r)), -DUSE_IPV6 -DAF_INET6=23 -DINET6_ADDRSTRLEN=46, )
 endif
 
+# set the default settings according to the target above
+$(set_target_defaults)
+
 #### Determine version, sub-version and release date.
 # If GIT is found, and IGNOREGIT is not set, VERSION, SUBVERS and VERDATE are
 # extracted from the last commit. Otherwise, use the contents of the files