lib: libc: Disable newlib on FVP SMP configurations for now

Newlib has systematic spinlock validation failures on ARM FVP SMP
configurations, manifesting as:

  ASSERTION FAIL [z_spin_lock_valid(l)]
  @ WEST_TOPDIR/zephyr/kernel/timeout.c:29
    - Caller: sys_clock_elapsed+0x28

This affects all newlib test variants on FVP SMP (tested on both v8a and
v9a configurations). The cause has yet to be found.

This change disables newlib support specifically for FVP SMP builds by
adding a dependency to NEWLIB_LIBC_SUPPORTED. This automatically filters
out all newlib test variants without requiring individual platform_exclude
entries in each testcase.yaml file.

Tests that failed with spinlock validation before this change:
- portability.posix.barriers.newlib
- portability.posix.clock_selection.newlib
- portability.posix.common.newlib
- portability.posix.common.tls.newlib
- portability.posix.eventfd.newlib
- portability.posix.fs.newlib
- portability.posix.headers.newlib
- portability.posix.rwlocks.newlib
- portability.posix.semaphores.newlib
- portability.posix.signals.newlib
- portability.posix.spinlocks.newlib
- portability.posix.threads_ext.newlib
- portability.posix.timers.newlib
- portability.posix.xsi_realtime.newlib
- portability.posix.xsi_single_process.newlib
- portability.posix.xsi_streams.newlib
- portability.posix.xsi_system_logging.newlib
- portability.posix.xsi_threads_ext.newlib
- libraries.libc.c11_threads.newlib
- libraries.libc.c11_threads.newlib_nano

Non-SMP FVP configurations and other ARM platforms are unaffected.

Signed-off-by: Nicolas Pitre <[email protected]>

Author: Nicolas Pitre

lib/libc/Kconfig

@@ -47,6 +47,9 @@ config NEWLIB_LIBC_SUPPORTED
 	bool
 	default y
 	depends on "$(TOOLCHAIN_HAS_NEWLIB)" = "y"
+	# Newlib has spinlock validation failures on FVP SMP configurations
+	# (ASSERTION FAIL [z_spin_lock_valid(l)] in sys_clock_elapsed())
+	depends on !(BOARD_FVP_BASE_REVC_2XAEM && SMP)
 	select FULL_LIBC_SUPPORTED
 	help
 	  Selected when the target has support for the newlib C library