matplotlib: import & fix cross-compile

The setupext.py code hardcodes a lot of paths to / which causes the code
to compile & link against the wrong things.  Change it to cross-compile
properly.

BUG=chromium:488089
TEST=`emerge-samux matplotlib` no longer links w/-L/usr/lib

Change-Id: Id248c30d1bc7d713e024bad08b1eadbf4e333b68
Reviewed-on: https://chromium-review.googlesource.com/271214
Tested-by: Mike Frysinger <vapier@chromium.org>
Reviewed-by: Simran Basi <sbasi@chromium.org>
diff --git a/dev-python/matplotlib/Manifest b/dev-python/matplotlib/Manifest
new file mode 100644
index 0000000..65a1610
--- /dev/null
+++ b/dev-python/matplotlib/Manifest
@@ -0,0 +1 @@
+DIST matplotlib-1.3.1.tar.gz 42163182 SHA256 ea16679d9476ab2757102e80327f31eb8e6c2cb09e2be89715c02e4e8fbdaf6a SHA512 04877aa15b6d52a6f813e8377098d13c432f66ae2522c544575440180944c9b73a2164ae63edd3a0eff807883bf7b39cd55f28454ccee8c76146567ff4a6fd40 WHIRLPOOL 18ba178eeef46e38d2c904e1be30a37e99321331ed47a7e63f592acb10f2a6c855be5dd600afcfc7cefaf9952acbc0a993e1d39b74287316abcb57b97e353261