hal_rpi_pico: require GNU extensions for pico SDK

[dancollins]

The pico SDK uses typeof() and the current approach, in CMakeLists.txt, wasn't enough. This commit adds a
dependency on GNU extensions to ensure the builds pass.

See #90936 for full details.

[josuah]

Short brainstorming:

• One way is to enable GNU extensions
• One way is to enable C23
• One way is this workaround:
  

  zephyr/arch/arm/include/cortex_m/cmse.h

  Lines 138 to 143 in cf6170c

  	/* Required for C99 compilation (required for GCC-8.x version,
  	* where typeof is used instead of __typeof__)
  	*/
  	#ifndef typeof
  	#define typeof __typeof__
  	#endif

More reading:

• Regulate GNUism in Zephyr codebase #52226

Thank you!

[sonarqubecloud]

Quality Gate passed

Issues
0 New issues
0 Accepted issues

Measures
0 Security Hotspots
0.0% Coverage on New Code
0.0% Duplication on New Code

See analysis details on SonarQube Cloud

[soburi]

zephyrproject-rtos/hal_rpi_pico#9
#90939
(And also reverting recent changes #90896)

This was discussed in the PR above, and unless there are any new issues that require a change in policy, we would like to proceed with the current situation.

Since pico-sdk requires gcc extensions or c24, we have no choice but to introduce this for the har_rpi_pico domain, but we would like to maintain c99 for the rest.

The current method is a bit hacky, but I think it's not bad from the perspective of achieving both of the above goals.

[dancollins]

I had searched for 'typeof' but didn't think to search for the C standard :) Thanks @josuah and @soburi.

Your approach, setting gnu11 for just the pico sources, is much less heavy-handed so I will close this.