MINOR: build: add aix72-gcc build TARGET and power{8,9} CPUs

As haproxy wont build on AIX 7.2 using the old "aix52" TARGET a new
TARGET was introduced which adds two special CFLAGS to prevent the
loading of AIXs xmem.h and var.h. This is done by defining the
corresponding include-guards _H_XMEM and _H_VAR. Without excluding
those headers-files the build fails because of redefinition errors:

1)
  CC      src/mux_fcgi.o
In file included from /usr/include/sys/uio.h:90,
                 from /opt/freeware/lib/gcc/powerpc-ibm-aix7.1.0.0/8.3.0/include-fixed/sys/socket.h:104,
                 from include/common/compat.h:32,
                 from include/common/cfgparse.h:25,
                 from src/mux_fcgi.c:13:
src/mux_fcgi.c:204:13: error: expected ':', ',', ';', '}' or '__attribute__' before '.' token
  struct ist rem_addr;
             ^~~~~~~~

2)
  CC      src/cfgparse-listen.o
In file included from include/types/arg.h:31,
                 from include/types/acl.h:29,
                 from include/types/proxy.h:41,
                 from include/proto/log.h:34,
                 from include/common/cfgparse.h:30,
                 from src/mux_h2.c:13:
include/types/vars.h:30:8: error: redefinition of 'struct var'
 struct var {
        ^~~

Futhermore, to enable multithreading via USE_THREAD, the atomic
library was added to the LDFLAGS. Finally, two new CPUs were added
to simplify the usage of power8 and power9 optimizations.

This TARGET was only tested on GCC 8.3 and may or may not work on
IBM's native C-compiler (XLC).

Should be backported to 2.1.

INSTALL

@@ -379,6 +379,7 @@ and assign it to the TARGET variable :
   - openbsd             for OpenBSD 5.7 and above
   - aix51               for AIX 5.1
   - aix52               for AIX 5.2
+  - aix72-gcc           for AIX 7.2 (using gcc)
   - cygwin              for Cygwin
   - haiku               for Haiku
   - generic             for any other OS or version.
@@ -391,6 +392,8 @@ one of the following choices to the CPU variable :
   - i686 for intel PentiumPro, Pentium 2 and above, AMD Athlon (32 bits)
   - i586 for intel Pentium, AMD K6, VIA C3.
   - ultrasparc : Sun UltraSparc I/II/III/IV processor
+  - power8 : IBM POWER8 processor
+  - power9 : IBM POWER9 processor
   - native : use the build machine's specific processor optimizations. Use with
     extreme care, and never in virtualized environments (known to break).
   - generic : any other processor or no CPU-specific optimization. (default)
@@ -516,6 +519,13 @@ this is easily addressed using the "aix52" target. If you get build errors
 because of strange symbols or section mismatches, simply remove -g from
 DEBUG_CFLAGS.
 
+Building on AIX 7.2 works fine using the "aix72-gcc" TARGET. It adds two
+special CFLAGS to prevent the loading of AIXs xmem.h and var.h. This is done
+by defining the corresponding include-guards _H_XMEM and _H_VAR. Without
+excluding those header-files the build fails because of redefinition errors.
+Futhermore, the atomic library is added to the LDFLAGS to allow for
+multithreading via USE_THREAD.
+
 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

Makefile

@@ -144,13 +144,13 @@ DOCDIR = $(PREFIX)/doc/haproxy
 # Use TARGET=<target_name> to optimize for a specifc target OS among the
 # following list (use the default "generic" if uncertain) :
 #    linux-glibc, linux-glibc-legacy, solaris, freebsd, openbsd, netbsd,
-#    cygwin, haiku, aix51, aix52, osx, generic, custom
+#    cygwin, haiku, aix51, aix52, aix72-gcc, osx, generic, custom
 TARGET =
 
 #### TARGET CPU
 # Use CPU=<cpu_name> to optimize for a particular CPU, among the following
 # list :
-#    generic, native, i586, i686, ultrasparc, custom
+#    generic, native, i586, i686, ultrasparc, power8, power9, custom
 CPU = generic
 
 #### Architecture, used when not building for native architecture
@@ -257,6 +257,8 @@ CPU_CFLAGS.native     = -O2 -march=native
 CPU_CFLAGS.i586       = -O2 -march=i586
 CPU_CFLAGS.i686       = -O2 -march=i686
 CPU_CFLAGS.ultrasparc = -O6 -mcpu=v9 -mtune=ultrasparc
+CPU_CFLAGS.power8     = -O2 -mcpu=power8 -mtune=power8
+CPU_CFLAGS.power9     = -O2 -mcpu=power9 -mtune=power9
 CPU_CFLAGS            = $(CPU_CFLAGS.$(CPU))
 
 #### ARCH dependant flags, may be overridden by CPU flags
@@ -381,7 +383,7 @@ ifeq ($(TARGET),aix51)
   DEBUG_CFLAGS    =
 endif
 
-# AIX 5.2 and above
+# AIX 5.2
 ifeq ($(TARGET),aix52)
   set_target_defaults = $(call default_opts, \
     USE_POLL USE_LIBCRYPT USE_OBSOLETE_LINKER)
@@ -389,6 +391,14 @@ ifeq ($(TARGET),aix52)
   DEBUG_CFLAGS    =
 endif
 
+# AIX 7.2 and above
+ifeq ($(TARGET),aix72-gcc)
+  set_target_defaults = $(call default_opts, \
+    USE_POLL USE_THREAD USE_LIBCRYPT USE_OBSOLETE_LINKER USE_GETADDRINFO)
+  TARGET_CFLAGS   = -D_H_XMEM -D_H_VAR
+  TARGET_LDFLAGS  = -latomic
+endif
+
 # Cygwin
 ifeq ($(TARGET),cygwin)
   set_target_defaults = $(call default_opts, \
@@ -754,7 +764,7 @@ all:
 	@echo "Please choose the target among the following supported list :"
 	@echo
 	@echo "   linux-glibc, linux-glibc-legacy, solaris, freebsd, openbsd, netbsd,"
-	@echo "   cygwin, haiku, aix51, aix52, osx, generic, custom"
+	@echo "   cygwin, haiku, aix51, aix52, aix72-gcc, osx, generic, custom"
 	@echo
 	@echo "Use \"generic\" if you don't want any optimization, \"custom\" if you"
 	@echo "want to precisely tweak every option, or choose the target which"
@@ -832,7 +842,7 @@ help:
 	   else \
 	     echo "TARGET not set, you may pass 'TARGET=xxx' to set one among :";\
 	     echo "  linux-glibc, linux-glibc-legacy, solaris, freebsd, netbsd, osx,"; \
-	     echo "  openbsd, aix51, aix52, cygwin, haiku, generic, custom"; \
+	     echo "  openbsd, aix51, aix52, aix72-gcc, cygwin, haiku, generic, custom"; \
 	   fi
 	$(Q)echo;echo "Enabled features for TARGET '$(TARGET)' (disable with 'USE_xxx=') :"
 	$(Q)set -- $(foreach opt,$(patsubst USE_%,%,$(use_opts)),$(if $(USE_$(opt)),$(opt),)); echo "  $$*" | (fmt || cat) 2>/dev/null