Can't install any version of PHP with Homebrew on Mac OS X 10.9.2

brew --config

HOMEBREW_VERSION: 0.9.5
ORIGIN: https://github.com/Homebrew/homebrew
HEAD: b10c09b1746cd5673bff4e40c4485cb266b1932b
HOMEBREW_PREFIX: /usr/local
HOMEBREW_CELLAR: /usr/local/Cellar
CPU: quad-core 64-bit ivybridge
OS X: 10.9.2-x86_64
Xcode: 5.1.1
CLT: 5.1.0.0.1.1396320587
GCC-4.2: build 5666
Clang: 5.1 build 503
X11: N/A
System Ruby: 1.8.7-358
Perl: /usr/bin/perl
Python: /usr/bin/python
Ruby: /usr/bin/ruby
Colins-MacBook-Pro:~ colin$

brew doctor

Warning: Unbrewed dylibs were found in /usr/local/lib.
If you didn't put them there on purpose they could cause problems when
building Homebrew formulae, and may need to be deleted.

Unexpected dylibs:
    /usr/local/lib/libmcrypt.4.4.8.dylib

Warning: Unbrewed .la files were found in /usr/local/lib.
If you didn't put them there on purpose they could cause problems when
building Homebrew formulae, and may need to be deleted.

Unexpected .la files:
    /usr/local/lib/libmcrypt.la

brew install php55

==> Downloading http://www.php.net/get/php-5.5.12.tar.bz2/from/this/mirror
Already downloaded: /Library/Caches/Homebrew/php55-5.5.12
Warning: Backing up all known pear.conf and .pearrc files
Warning: If you have a pre-existing pear install outside
         of homebrew-php, or you are using a non-standard
         pear.conf location, installation may fail.
==> ./configure --prefix=/usr/local/Cellar/php55/5.5.12 --localstatedir=/usr/loc
checking for mmap() using shm_open() shared memory support... no
checking for mmap() using regular file shared memory support... no
checking "whether flock struct is linux ordered"... "no"
checking "whether flock struct is BSD ordered"... "no"
configure: error: Don't know how to define struct flock on this system, set --enable-opcache=no

READ THIS: https://github.com/Homebrew/homebrew/wiki/troubleshooting
If reporting this issue please do so at (not Homebrew/homebrew):
  https://github.com/josegonzalez/homebrew-homebrew-php/issues