Fix #1006: Disable Objective-C in clang-format

[jeroenbakker-atmind]

Description

fixes #1006

Regression introduced by iOS support. The clang format configuration file doesn't contain a section for
objective-c files and using script/clang-format.py would fail because it cannot exclude objective-c
files based on extension alone.

Both CPP and ObjectiveC uses the same extension for their header files (.h)
This has been fixed by adding a configuration section to .clang-format to ignore Objective-C
files.

Eventually we should improve the configuration. for example use LLVM style for Objective-C

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