python: fix ctypes.util.find_library() with musl; patch from Alpine.

This patch should also work for glibc, so that it's applied unconditionally.
It's unfortunate that this code on glibc relies on `ldconfig -p` to work
correctly.

srcpkgs/python/patches/musl-find_library.patch

@@ -0,0 +1,43 @@
+See http://bugs.alpinelinux.org/issues/4512
+
+--- Lib/ctypes/util.py
++++ Lib/ctypes/util.py
+@@ -238,8 +238,37 @@ elif os.name == "posix":
+                 return None
+             return res.group(1)
+ 
++        def _is_elf(filepath):
++            try:
++                with open(filepath, 'rb') as fh:
++                    return fh.read(4) == b'\x7fELF'
++            except:
++                return False
++
++        def _find_libfile(name):
++            from glob import glob
++            # special case for libm, libcrypt and libpthread and musl
++            if name in ['m', 'crypt', 'pthread']:
++                name = 'c'
++            elif name in ['libm.so', 'libcrypt.so', 'libpthread.so']:
++                name = 'libc.so'
++            # search in standard locations
++            paths = ['/lib', '/usr/lib', '/usr/local/lib']
++            if 'LD_LIBRARY_PATH' in os.environ:
++                paths = os.environ['LD_LIBRARY_PATH'].split(':') + paths
++            for d in paths:
++                f = os.path.join(d, name)
++                if _is_elf(f):
++                    return f
++
++                prefix = os.path.join(d, 'lib'+name)
++                for suffix in ['.so', '.so.*', '.*.so.*']:
++                    for f in glob('{0}{1}'.format(prefix, suffix)):
++                        if _is_elf(f):
++                            return f
++
+         def find_library(name):
+-            return _findSoname_ldconfig(name) or _get_soname(_findLib_gcc(name))
++            return _find_libfile(name) or _findSoname_ldconfig(name) or _get_soname(_findLib_gcc(name))
+ 
+ ################################################################
+ # test code

srcpkgs/python/template

@@ -4,7 +4,7 @@
 #
 pkgname=python
 version=2.7.10
-revision=6
+revision=7
 wrksrc="Python-${version}"
 hostmakedepends="pkg-config"
 makedepends="