make it possible to use clang-tidy

Contains a .jq script that mangles build/compile_commands.json in a way that is suitable for consumption by clang:

• remove unknown command line options
• add -m32 switch
• make paths absolute (better for some IDEs)

tools/compile_commands.jq

+[.[]|({
+    directory:.directory,
+    command:(. as {file:$file, directory:$directory}
+        |.command
+        |sub("-fno-isolate-erroneous-paths-dereference";"-m32")
+        |sub("(?<a>\\s)\\.\\./"; (.a) + "\($directory)/../")
+        |sub("/build/\\.\\./"; "/")
+        )
+    ,
+    file:((.directory|sub("build$";""))+(.file|sub("^../";"")))
+})]