This is a followup to 009b53fd.
* gnu/packages/patches/python-3-search-paths.patch: Check
'C_INCLUDE_PATH' instead of 'CPATH'.
* gnu/packages/patches/python-2.7-search-paths.patch: Likewise.
* gnu/packages/patches/python-2.7-search-paths.patch,
gnu/packages/patches/python-3-search-paths.patch: New files.
* gnu-system.am (dist_patch_DATA): Add them.
* gnu/packages/python.scm (python-2)[source]: Use first patch.
[arguments]: Remove now unneeded CPPFLAGS and LDFLAGS.
(python)[source]: Use second patch.
(python-minimal)[arguments]: Remove CPPFLAGS and LDFLAGS.