C99/C++03 standard compliance

[geky]

Currently, there are no barriers in place for using compiler extensions. This makes it difficult to know when code is inherently unportable. Allowing compiler extensions hurts reproducibility across toolchains.

From previous discussions these appear to be our target standards:

• C99
• C++03 (C++11 is unsupported in IAR)

Here is a quick checklist of what is needed to bring mbed up to compliance:

• strict c99/c++03 flags in gcc
• strict c99/c++03 flags in armc5
• strict c99/c++03 flags in iar
• compile in gcc
• compile in armc5
• compile in iar
• warning free in gcc
• warning free in armc5
• warning free in iar

Previous issue: #241

[geky]

From the conversation here: #241

Selecting --std=c99 or --std=c++98 is not sufficient to enforce language standard conformance, since these options tell gcc to accept the base language standard and any gnu extensions that do not conflict with the base language standard.

In order to enforce language standard conformance the compiler must IIRC be given the -pedantic option along with the --std=c99 or --std=c++98 option.

For gcc the strict flags seem to be --std=c99 -pedantic and --std=c++98 -pedantic. If anyone knows the appropriate flags for armc5 or iar, let me know.

I am currently working out of a branch over here:
https://github.com/geky/mbed/tree/pedantic

Here is the current output when compiling mbed as a library for the K64F:
https://gist.github.com/geky/2fb606eb757685a9f36e6c4b6064834a

[geky]

According to the iar language standard page (here), iar fully supports c++03.

It's an incredibly unnoticable update to the language, mostly defect fixes (wiki) and I see no reason to not adopt it. So baring any complaints I'm going to go ahead and bump the c++ standard to c++03.

Updated gcc flags to --std=c++03 -pedantic.

[ciarmcom]

ARM Internal Ref: IOTMORF-133