Tweak linux_glibc properties for musl builds in external/python/cpython2

For convenience, builds against musl libc currently use the
linux_glibc properties because they are almost always linux-specific
and not glibc-specific.  In preparation for removing this hack,
tweak the linux_glibc properties by either moving them to host_linux,
which will apply to linux_glibc, linux_musl and linux_bionic, or
by setting appropriate musl or linux_musl properties.  Properties
that must not be repeated while musl uses linux_musl and also still
uses the linux_glibc properties are moved to glibc properties, which
don't apply to musl.  Whether these stay as glibc properties or get
moved back to linux_glibc later once the musl hack is removed is TBD.

Bug: 223257095
Test: m checkbuild
Test: m USE_HOST_MUSL=true host-native
Change-Id: I1738c5a0e89f5c686eda7fa63da3c2583540dca8
diff --git a/Android.bp b/Android.bp
index 0289573..b13d7e4 100644
--- a/Android.bp
+++ b/Android.bp
@@ -114,10 +114,17 @@
         linux_glibc_x86: {
             enabled: false,
         },
+        linux_musl_x86: {
+            enabled: false,
+        },
         linux_glibc_x86_64: {
             local_include_dirs: ["linux_x86_64/pyconfig"],
             cflags: ["-Werror"],
         },
+        linux_musl_x86_64: {
+            local_include_dirs: ["linux_x86_64/pyconfig"],
+            cflags: ["-Werror"],
+        },
         windows: {
             enabled: false,
         },
@@ -976,13 +983,7 @@
                 "Modules/_ctypes/libffi/src/x86/darwin64.S",
             ],
         },
-        linux_bionic: {
-            local_include_dirs: ["linux_x86_64/libffi"],
-            srcs: [
-                "Modules/_ctypes/libffi/src/x86/unix64.S",
-            ],
-        },
-        linux_glibc_x86_64: {
+        host_linux: {
             local_include_dirs: ["linux_x86_64/libffi"],
             srcs: [
                 "Modules/_ctypes/libffi/src/x86/unix64.S",