lib/libc: Mark picolibc as providing full C library support

Select FULL_LIBC_SUPPORTED when picolibc is available.

Add picolibc as a secondary default C library when REQUIRES_FULL_LIBC is
selected. This is necessary as tests gated on FULL_LIBC_SUPPORTED need to
be sure that a full C library will be selected -- if only picolibc is
available, those tests will need to select that.

This should permit use of a picolibc-only crosstool-ng toolchain in
testing.

Signed-off-by: Keith Packard <[email protected]>

Author: keith-packard

lib/libc/Kconfig

@@ -39,6 +39,7 @@ config PICOLIBC_SUPPORTED
 	depends on !(CPP && "$(ZEPHYR_TOOLCHAIN_VARIANT)" = "zephyr")
 	# picolibc text is outside .pinned.text on this board. #54148
 	default y
+	select FULL_LIBC_SUPPORTED
 	help
 	  Selected when the target has support for picolibc.
 
@@ -55,6 +56,7 @@ choice LIBC_IMPLEMENTATION
 	prompt "C Library Implementation"
 	default EXTERNAL_LIBC if NATIVE_APPLICATION
 	default NEWLIB_LIBC if REQUIRES_FULL_LIBC
+	default PICOLIBC if REQUIRES_FULL_LIBC
 	default MINIMAL_LIBC
 
 config MINIMAL_LIBC