Join build makefiles together

Changes:
- Joins build/build.mk and build/build2.mk files together since there
  isn't any practical reason for having two different files with the
  current build system.
- Makefile is now more portable. All special syntaxes are omitted, for
  example, a conditional assignment operators `?=`. This makes buildconf
  more useful on Solaris make derivative, so there is no longer need to
  override make with gmake: `MAKE=gmake ./buildconf`.
- Suppressing autoconf and autoheader warnings is not needed anymore
  with current build system. Instead, the option `-Wall` has been used
  when running `./buildconf --debug` to get more useful debug info
  about current M4.

buildconf

@@ -3,6 +3,8 @@
 # A wrapper around Autoconf that generates files to build PHP on *nix systems.
 
 MAKE=${MAKE:-make}
+PHP_AUTOCONF=${PHP_AUTOCONF:-autoconf}
+PHP_AUTOHEADER=${PHP_AUTOHEADER:-autoheader}
 force=0
 debug=0
 
@@ -91,11 +93,14 @@ fi
 
 echo "buildconf: Building configure files"
 
-# List of *.m4 prerequisites files for the make configure target.
-M4_FILES=$(echo TSRM/*.m4 Zend/*.m4 ext/*/config*.m4 sapi/*/config*.m4)
-
 if test "$debug" = "1"; then
-  $MAKE -s -f build/build.mk M4_FILES="$M4_FILES" SUPPRESS_WARNINGS=""
+  autoconf_flags="-f -Wall"
 else
-  $MAKE -s -f build/build.mk M4_FILES="$M4_FILES"
+  autoconf_flags="-f"
 fi
+
+$MAKE -s -f build/build.mk \
+  PHP_AUTOCONF="$PHP_AUTOCONF" \
+  PHP_AUTOHEADER="$PHP_AUTOHEADER" \
+  PHP_AUTOCONF_FLAGS="$autoconf_flags" \
+  PHP_M4_FILES="$(echo TSRM/*.m4 Zend/*.m4 ext/*/config*.m4 sapi/*/config*.m4)"