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Specify command-line options with an environment variable

The ARMCC5_ASMOPT environment variable can hold command-line options for the assembler.

The syntax is identical to the command-line syntax. The assembler reads the value of ARMCC5_ASMOPT and inserts it at the front of the command string. This means that options specified in ARMCC5_ASMOPT can be overridden by arguments on the command line.