Rename target.linux[_x86[_64]] to target.linux_glibc[_x86[_64]]

In the future, target.linux will apply to all targets running a linux kernel
(android, linux_glibc, linux_bionic). So move all current users to the specific
linux_glibc.

There will be another cleanup pass later that will move some instances back to
target.linux if the properties should be shared with target.android and
target.linux_bionic, but target.linux needs to be removed first.

Test: out/soong/build.ninja identical before/after
Change-Id: I7ea3d000c5bcfb6f9c79438e944212a998ab5284
Exempt-From-Owner-Approval: build system cleanup
diff --git a/Lib/Android.bp b/Lib/Android.bp
index 1d89a1b..3a90571 100644
--- a/Lib/Android.bp
+++ b/Lib/Android.bp
@@ -48,7 +48,7 @@
         darwin: {
             srcs: [":py2-plat-darwin"],
         },
-        linux_x86_64: {
+        linux_glibc_x86_64: {
             srcs: [":py2-plat-linux2"],
         },
     },