When installing apc on a fresh rhel4 x86_64 kick, autoconfig failed with the following:

[161472-app1 18:22:17]-(/var/lib/mysql)# pecl install apc
 downloading APC-3.0.18.tgz ...
 Starting to download APC-3.0.18.tgz (115,957 bytes)
 .........................done: 115,957 bytes
 47 source files, building
 running: phpize
 Configuring for:
 PHP Api Version:         20041225
 Zend Module Api No:      20060613
 Zend Extension Api No:   220060519
 1. Use apxs to set compile flags (if using APC with Apache)? : yes
1-1, 'all', 'abort', or Enter to continue: all
 Use apxs to set compile flags (if using APC with Apache)? [yes] :
 1. Use apxs to set compile flags (if using APC with Apache)? : yes
1-1, 'all', 'abort', or Enter to continue:
 building in /var/tmp/pear-build-root/APC-3.0.18
 running: /tmp/pear/temp/APC/configure --with-apxs
 checking for egrep... grep -E
 checking for a sed that does not truncate output... /bin/sed
 checking for gcc... gcc
 checking for C compiler default output file name... a.out
 checking whether the C compiler works... yes
 checking whether we are cross compiling... no
 checking for suffix of executables...
 checking for suffix of object files... o
 checking whether we are using the GNU C compiler... yes
 checking whether gcc accepts -g... yes
 checking for gcc option to accept ANSI C... none needed
 checking whether gcc and cc understand -c and -o together... yes
 checking for system library directory... lib
 checking if compiler supports -R... no
 checking if compiler supports -Wl,-rpath,... yes
 checking build system type... x86_64-redhat-linux-gnu
 checking host system type... x86_64-redhat-linux-gnu
 checking target system type... x86_64-redhat-linux-gnu
 checking for PHP prefix... /usr
 checking for PHP includes... -I/usr/include/php -I/usr/include/php/main -I/usr/include/php/TSRM -I/usr/include/php/Zend -I/usr/include/php/ext -I/usr/include/php/ext/date/lib
 checking for PHP extension directory... /usr/lib64/php/modules
 checking for PHP installed headers prefix... /usr/include/php
 checking for re2c... no
 configure: WARNING: You will need re2c 0.12.0 or later if you want to regenerate PHP parsers.
 checking for gawk... gawk
 checking whether apc needs to get compiler flags from apxs...
Sorry, I was not able to successfully run APXS.  Possible reasons:
1.  Perl is not installed;
 2.  Apache was not compiled with DSO support (--enable-module=so);
 3.  'apxs' is not in your path.  Try to use --with-apxs=/path/to/apxs
 The output of /usr/sbin/apxs follows
 Can't exec "/usr/bin/apr-config": No such file or directory at /usr/sbin/apxs line 48.
 Use of uninitialized value in scalar chomp at /usr/sbin/apxs line 53.
 apxs:Error: /usr/bin/apr-config not found!.
 -O2 -g -pipe -m64
 configure: error: Aborting
 ERROR: `/tmp/pear/temp/APC/configure --with-apxs' failed

Solution:

# up2date apr-devel
# up2date apr-util-devel