Support for Precompiled Header (PCH) files is
deprecated from ARM Compiler 5.05 onwards on all platforms. Note that ARM Compiler
on Windows 8 never supported PCH files.
PCH file processing means that the compiler automatically
looks for a qualifying PCH file, and reads it if found. Otherwise,
the compiler creates one for use on a subsequent compilation.
When the compiler creates a PCH file, it takes the name of
the primary source file and replaces the suffix with .pch.
The PCH file is created in the directory of the primary source file
--pch_dir option is specified.