Move linux to //third_party.

Test Plan: refactor of build system, should be covered by existing tests

X-Origin-Diff: phab/D367
GitOrigin-RevId: 603c61bfadadfbd66c0ce31f05f6748251bea9f3
diff --git a/core/build/utils/BUILD b/core/build/utils/BUILD
index d49359a..9a8dc68 100644
--- a/core/build/utils/BUILD
+++ b/core/build/utils/BUILD
@@ -27,7 +27,7 @@
         "@xfsprogs_dev//:all",
         "@musl//:all",
         "@util_linux//:all",
-        "@linux_kernel//:all",
+        "@linux//:all",
     ],
     outs = [
         "mkfs.xfs",
@@ -44,7 +44,7 @@
 
     echo "Installing Linux kernel headers..."
     (
-        cd external/linux_kernel
+        cd external/linux
         make headers_install ARCH=x86_64 INSTALL_HDR_PATH=$$MUSL
     ) > /dev/null