lkl: add support for LKL_INSTALL_ADDITIONAL_HEADERS environment variable

this environment variable contains a path to a file with a list of
additional header files to install when running "make install".

- The file contains one header per line.
- empty lines are permitted
- '#' comments are supported - even inline

Signed-off-by: Michael Zimmermann <sigmaepsilon92@gmail.com>

arch/lkl/scripts/headers_install.py

@@ -129,6 +129,13 @@ def replace(h):
 find_headers("arch/lkl/include/uapi/asm/syscalls.h")
 headers.add("arch/lkl/include/uapi/asm/host_ops.h")
 
+if 'LKL_INSTALL_ADDITIONAL_HEADERS' in os.environ:
+    with open(os.environ['LKL_INSTALL_ADDITIONAL_HEADERS'], 'rU') as f:
+        for line in f.readlines():
+            line = line.split('#', 1)[0].strip()
+            if line != '':
+                headers.add(line)
+
 new_headers = set()
 
 for h in headers: