meta: add tool to combine multiple compile-commands database files

this allows once instance of an lsp to understand multiple
cmake build directories.

util/merge-compiledb.py

@@ -0,0 +1,24 @@
+#!/usr/bin/env python3
+import sys
+import json
+
+if len(sys.argv) < 3:
+    print('USAGE: {} <dest-file> [src-files...]'.format(sys.argv[0]))
+    exit(-1)
+
+dest_path = sys.argv[1]
+src_paths = sys.argv[2:]
+
+dest = open(dest_path, 'r')
+dest_data = json.load(dest)
+dest.close()
+
+for src_path in src_paths:
+    src = open(src_path, 'r')
+    src_data = json.load(src)
+    dest_data += src_data
+    src.close()
+
+dest = open(dest_path, 'w')
+json.dump(dest_data, dest, indent=4)
+dest.close()