libc: Update auto-gen scripts

Make the scripts use external/kernel-headers/original by default.

clean_header.py:  Document -k<path>, add -d<path>
find_headers.py:  Make kernel config files optional
update_all.py:    Allow setting the path to kernel headers on the command-line
update_all.py:    Better formatting of output on ttys
update_all.py:    Automatically perform "git add/rm" on affected files.
SYSCALLS.TXT:     Fix typo in __socketcall definition.
checksyscalls.py: Add support for superH architecture in the checks.
gensyscalls.py:   Automatically perform "git add/rm" on affected files.
cpp.py:           Fixed a bug that prevented certain type definitions to
                  be kept in the generated clean header (e.g.
                  struct ethtool_drvinfo in <linux/ethtool.h>)

All scripts will use the content of external/kernel-headers/original by default now.

The generated code removes all empty lines and trailing whitespace. This is useful
to ensure a unified output even if we change the parser again in the future.

The top-level disclaimer has been edited with update instructions to regenerate
the headers when needed.

Also, a warning is now inserted every 8th line in the final output:

/* WARNING: DO NOT EDIT, AUTO-GENERATED CODE - SEE TOP FOR INSTRUCTIONS */

Changes under kernel/arch-arm and kernel/arch-x86 should correspond to whitespace
differences and additionnal struct definitions that were missed by the previous
parser implementation.

Change-Id: Icd1c056bacd766759f3e9b7bb5d63a246f3d656a

WARNING: If you run these script, do not submit the result to gerrit for now.
         It seems there are discrepancies between the content of original headers
         and those currently commited under bionic/libc/kernel/.

         (This problem is the main motivation to insert the warning repeatedly).

         Current list of issues:

           - Missing SuperH headers (i.e. external/kernel-headers/original/asm-sh)
diff --git a/libc/kernel/tools/defaults.py b/libc/kernel/tools/defaults.py
index 5e9d6770..2bee4ec 100644
--- a/libc/kernel/tools/defaults.py
+++ b/libc/kernel/tools/defaults.py
@@ -16,7 +16,11 @@
 
 # path to the directory containing the original kernel headers
 #
-kernel_original_path = os.path.normpath( find_program_dir() + '/../original' )
+kernel_original_path = os.path.normpath( find_program_dir() + '/../../../../external/kernel-headers/original' )
+
+# path to the default location of the cleaned-up headers
+#
+kernel_cleaned_path = os.path.normpath( find_program_dir() + '/..' )
 
 # a special value that is used to indicate that a given macro is known to be
 # undefined during optimization
@@ -112,6 +116,18 @@
  ***   structures, and macros generated from the original header, and thus,
  ***   contains no copyrightable information.
  ***
+ ***   To edit the content of this header, modify the corresponding
+ ***   source file (e.g. under external/kernel-headers/original/) then
+ ***   run bionic/libc/kernel/tools/update_all.py
+ ***
+ ***   Any manual change here will be lost the next time this script will
+ ***   be run. You've been warned!
+ ***
  ****************************************************************************
  ****************************************************************************/
 """
+
+# This is the warning line that will be inserted every N-th line in the output
+kernel_warning = """\
+/* WARNING: DO NOT EDIT, AUTO-GENERATED CODE - SEE TOP FOR INSTRUCTIONS */
+"""