Move Autoconf Archive macros to a common m4 dir

In PHP the build dir is used as a directory for external macros
including Autoconf Archive macros.

CONTRIBUTING.md

@@ -124,19 +124,15 @@ locations.
 ```bash
 <php-src>/
  ├─ .git/                           # Git configuration and source directory
- └─ TSRM/                           # Thread Safe Resource Manager
-    └─ m4/                          # https://github.com/autoconf-archive/autoconf-archive
-       └─ ax_func_which_gethostbyname_r.m4
-    └─ ...
+ ├─ TSRM/                           # Thread Safe Resource Manager
  └─ Zend/                           # Zend Engine
     ├─ zend_vm_execute.h            # Generated by `Zend/zend_vm_gen.php`
     ├─ zend_vm_opcodes.c            # Generated by `Zend/zend_vm_gen.php`
     ├─ zend_vm_opcodes.h            # Generated by `Zend/zend_vm_gen.php`
     └─ ...
  ├─ appveyor/                       # Appveyor CI service files
  └─ build/                          # *nix build system files
-    ├─ ax_check_compile_flag.m4     # https://github.com/autoconf-archive/autoconf-archive
-    ├─ ax_gcc_func_attribute.m4     # https://github.com/autoconf-archive/autoconf-archive
+    ├─ ax_*.m4                      # https://github.com/autoconf-archive/autoconf-archive
     ├─ config.guess                 # https://git.savannah.gnu.org/cgit/config.git
     ├─ config.sub                   # https://git.savannah.gnu.org/cgit/config.git
     ├─ libtool.m4                   # https://git.savannah.gnu.org/cgit/libtool.git

TSRM/tsrm.m4

@@ -1,17 +1,11 @@
-m4_include([TSRM/m4/ax_func_which_gethostbyname_r.m4])
-
 AC_DEFUN([TSRM_BASIC_CHECKS],[
 
 AC_REQUIRE([AC_PROG_CC])dnl
 AC_REQUIRE([AC_PROG_RANLIB])dnl
 
 AC_CHECK_FUNCS(sigprocmask)
-
-AX_FUNC_WHICH_GETHOSTBYNAME_R()
-
 ])
 
-
 AC_DEFUN([TSRM_CHECK_PTH],[
 
 AC_MSG_CHECKING(for GNU Pth)

configure.ac

@@ -4,6 +4,7 @@ dnl Include external macro definitions before the AC_INIT to also remove
 dnl comments starting with # and empty newlines from the included files.
 dnl -------------------------------------------------------------------------
 m4_include([build/ax_check_compile_flag.m4])
+m4_include([build/ax_func_which_gethostbyname_r.m4])
 m4_include([build/ax_gcc_func_attribute.m4])
 m4_include([build/libtool.m4])
 m4_include([build/php_cxx_compile_stdcxx.m4])
@@ -664,6 +665,8 @@ asprintf \
 nanosleep \
 )
 
+AX_FUNC_WHICH_GETHOSTBYNAME_R
+
 dnl Some systems (like OpenSolaris) do not have nanosleep in libc
 PHP_CHECK_FUNC_LIB(nanosleep, rt)