```ruby
require 'formula'

class Gmp4 < Formula
  homepage 'http://gmplib.org/'
  url 'ftp://ftp.gmplib.org/pub/gmp-4.3.2/gmp-4.3.2.tar.bz2'
  sha1 'c011e8feaf1bb89158bd55eaabd7ef8fdd101a2c'

  option '32-bit'
  option 'skip-check', 'Do not run `make check` to verify libraries'

  def install
    # Reports of problems using gcc 4.0 on Leopard
    # https://github.com/mxcl/homebrew/issues/issue/2302
    # Also force use of 4.2 on 10.6 in case a user has changed the default
    ENV.gcc_4_2

    args = ["--prefix=#{prefix}", "--enable-cxx"]

    # Build 32-bit where appropriate, and help configure find 64-bit CPUs
    if MacOS.prefer_64_bit? and not build.build_32_bit?
      ENV.m64
      args << "--build=x86_64-apple-darwin"
    else
      ENV.m32
      args << "--host=none-apple-darwin"
    end

    system "./configure", *args
    system "make"
    ENV.j1 # Doesn't install in parallel on 8-core Mac Pro
    system "make install"

    # Different compilers and options can cause tests to fail even
    # if everything compiles, so yes, we want to do this step.
    system "make check" unless build.include? "skip-check"
  end
end
```

Fix legacy (not working) compiler check.
user
```ruby
require 'formula'

class Gmp4 < Formula
  homepage 'http://gmplib.org/'
  url 'ftp://ftp.gmplib.org/pub/gmp-4.3.2/gmp-4.3.2.tar.bz2'
  sha1 'c011e8feaf1bb89158bd55eaabd7ef8fdd101a2c'

  keg_only "Conflicts with gmp in main repository."

  option '32-bit'
  option 'skip-check', 'Do not run `make check` to verify libraries'

  fails_with :gcc_4_0 do
    cause "Reports of problems using gcc 4.0 on Leopard: https://github.com/mxcl/homebrew/issues/issue/2302"
  end

  def install
    args = ["--prefix=#{prefix}", "--enable-cxx"]

    # Build 32-bit where appropriate, and help configure find 64-bit CPUs
    if MacOS.prefer_64_bit? and not build.build_32_bit?
      ENV.m64
      args << "--build=x86_64-apple-darwin"
    else
      ENV.m32
      args << "--host=none-apple-darwin"
    end

    system "./configure", *args
    system "make"
    ENV.j1 # Doesn't install in parallel on 8-core Mac Pro
    system "make install"

    # Different compilers and options can cause tests to fail even
    # if everything compiles, so yes, we want to do this step.
    system "make check" unless build.include? "skip-check"
  end
end
```
assistant