FROMLIST: libcamera: base: Remove custom __nodiscard attribute

__nodiscard was introduced for compatibility with C++14. In C++17, there is an official attribute: nodiscard. Moreover, some libc implementations (like bionic) already define the __nodiscard macro [1].

Since:

• libcamera builds with cpp_std=c++17
• nodiscard is already used in the android HAL (exif)

We should replace all usage __nodiscard of by nodiscard for consistency.

Do the replacement and remove the no longer used compiler.h.

[1] https://android-review.googlesource.com/c/platform/bionic/+/3254860

Series:

• baylibre/ti/android/aosp/manifest!102 (merged)
• baylibre/ti/android/aosp/hardware/ti/am62x!20 (merged)
• !6 (merged)

/cc @glaroque @mfournier @nkbelin