Clean up header files from kernel directory.

Add a make distclean for each supported arch before generating headers
and at the end so these files are not left hanging around in the
kernel directory.

Bug: 174795055

Test: Verified all generated files are deleted after running.
Test: Verified this generates the exact same files as before this change.
Change-Id: I0f66f580af2ea50c190eb532032017e782d7cae6
diff --git a/libc/kernel/tools/generate_uapi_headers.sh b/libc/kernel/tools/generate_uapi_headers.sh
index 4e7d2af..7e49cde 100755
--- a/libc/kernel/tools/generate_uapi_headers.sh
+++ b/libc/kernel/tools/generate_uapi_headers.sh
@@ -218,12 +218,11 @@
 fi
 
 if [[ ${SKIP_GENERATION} -eq 0 ]]; then
-  # Clean up any leftover headers.
-  make distclean
-
   # Build all of the generated headers.
   for arch in "${ARCH_LIST[@]}"; do
     echo "Generating headers for arch ${arch}"
+    # Clean up any leftover headers.
+    make ARCH=${arch} distclean
     make ARCH=${arch} headers_install
   done
 fi
@@ -269,3 +268,12 @@
                      "${ANDROID_KERNEL_DIR}/scsi" \
                      "${KERNEL_DIR}"
 echo "Headers updated."
+
+if [[ ${SKIP_GENERATION} -eq 0 ]]; then
+  cd "${KERNEL_DIR}"
+  # Clean all of the generated headers.
+  for arch in "${ARCH_LIST[@]}"; do
+    echo "Cleaning kernel files for arch ${arch}"
+    make ARCH=${arch} distclean
+  done
+fi