Some options are not valid for the Thumb compiler. Make sure that you choose valid options, otherwise, the files might not compile.Compiler
(Project Properties window)
*.prj\COMPILE\Compilation\Compiler
Specify the compiler. Can be set to any of the following:
ARM_C the default
Thumb_C
ARM_Cpp
Thumb_Cpp
For more information about the options available when invoking the ARM Compiler, see the documentation for your toolchain.
Some options are not valid for the Thumb compiler. Make sure that you choose valid options, otherwise, the files might not compile.