IAR assembler 7.80 has some problems handling difficult macros, leading
to immediate exit with return value -11.
In particular, a URL string has been causing problems, presumably due to
the "//" resembling a comment.
A previous escaping workaround in 0d97803 seemed to work, but the crash
has still been seen with a particular target.
Previous creation of the extended command line file for the IAR
assembler was stripping quotes from macros. This rendered the resulting
definitions for string-containing macros incorrect, which means that we
can assume no assembler code is currently relying on them.
Therefore, as a precautionary measure to avoid the crash, simply remove
all macros containing strings when creating them for IAR. This
apparently clears the crashes seen during testing of
https://github.com/ARMmbed/mbed-os/pull/8023