py2cairo: fix miscompile on Lion. Use LINKFLAG.

waf miscompiles py2cairo on Lion, linking the wrong Python Library when
HB Python is installed.  So add a LINKFLAG that sets the path to the real
python Library as determined by `python-prefix`, where it gets used at
link time and fixes the problem where you can't import cairo into Python.
Also add a `fails_with :llvm` block to work around a build error where
waf tries to optimize with `-march=native` which llvm doesn't accept.

https://bugs.freedesktop.org/show_bug.cgi?id=51544

Tested on Lion and SL using system Python, HB framework Python,
HB non-framework Python with clang building both native and
universal binaries, by importing the cairo module into Python.

Rebased on Homebrew 0.9.2

Fixes Homebrew/homebrew#12893

Closes Homebrew/homebrew#12943.

Signed-off-by: Jack Nagel <jacknagel@gmail.com>

Formula/py2cairo.rb

@@ -8,6 +8,11 @@ class Py2cairo < Formula
   depends_on 'cairo'
   depends_on :x11
 
+  fails_with :llvm do
+    build 2336
+    cause "The build script will set -march=native which llvm can't accept"
+  end
+
   def options
     [['--universal', 'Build universal binaries']]
   end
@@ -22,7 +27,24 @@ class Py2cairo < Formula
       end
     end
 
+    # waf miscompiles py2cairo on Lion, linking the wrong Python Library when
+    # HB Python is installed.  So add a LINKFLAG that sets the path to the real
+    # python Library as determined by `python-prefix`, where it gets used at
+    # link time and fixes the problem where you can't import cairo into Python.
+    # https://github.com/mxcl/homebrew/issues/12893
+    # https://bugs.freedesktop.org/show_bug.cgi?id=51544
+    ENV['LINKFLAGS'] = "-L#{%x(python-config --prefix).chomp}/lib"
     system "./waf", "configure", "--prefix=#{prefix}", "--nopyc", "--nopyo"
     system "./waf", "install"
   end
+
+  def caveats; <<-EOS.undent
+    For non-homebrew Python, you need to amend your PYTHONPATH like so:
+      export PYTHONPATH=#{HOMEBREW_PREFIX}/lib/#{which_python}/site-packages:$PYTHONPATH
+    EOS
+  end
+
+  def which_python
+    "python" + `python -c 'import sys;print(sys.version[:3])'`.strip
+  end
 end