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: Ib89cce2ed559701bac953c91444bedcd2aa89030
Exempt-From-Owner-Approval: build system cleanup
diff --git a/NativeCode.bp b/NativeCode.bp
index 050f29f..3f296fa 100644
--- a/NativeCode.bp
+++ b/NativeCode.bp
@@ -113,7 +113,7 @@
     static_libs: ["libfdlibm"],
 
     target: {
-        linux: {
+        linux_glibc: {
             cflags: [ // Sigh.
                 "-D_LARGEFILE64_SOURCE",
                 "-D_GNU_SOURCE",