BUILD: enable poll() by default in the makefile

This allows to build haproxy for unknown targets and still have poll().
If for any reason a target does not support it, just passing USE_POLL=""
disables it.

Makefile

@@ -192,7 +192,10 @@ LDFLAGS = $(ARCH_FLAGS) -g
 # Depending on the target platform, some options are set, as well as some
 # CFLAGS and LDFLAGS. The USE_* values are set to "implicit" so that they are
 # not reported in the build options string. You should not have to change
-# anything there.
+# anything there. poll() is always supported, unless explicitly disabled by
+# passing USE_POLL="" on the make command line.
+USE_POLL   = default
+
 ifeq ($(TARGET),generic)
   # generic system target has nothing specific
   USE_POLL   = implicit

README

@@ -12,7 +12,7 @@
 To build haproxy, you will need :
   - GNU make. Neither Solaris nor OpenBSD's make work with the GNU Makefile.
     However, specific Makefiles for BSD and OSX are provided.
-  - GCC between 2.91 and 4.5.0. Others may work, but not tested.
+  - GCC between 2.91 and 4.7. Others may work, but not tested.
   - GNU ld
 
 Also, you might want to build with libpcre support, which will provide a very
@@ -138,6 +138,13 @@ otherwise __fd_select() will be used while not being present in the libc.
 If you get build errors because of strange symbols or section mismatches,
 simply remove -g from DEBUG_CFLAGS.
 
+You can easily define your own target with the GNU Makefile. Unknown targets
+are processed with no default option except USE_POLL=default. So you can very
+well use that property to define your own set of options. USE_POLL can even be
+disabled by setting USE_POLL="". For example :
+
+    $ gmake TARGET=tiny USE_POLL="" TARGET_CFLAGS=-fomit-frame-pointer
+
 
 2) How to install it
 --------------------