libc/picolibc: Set __LINUX_ERRNO_EXTENSIONS__ for picolibc

This makes sure extra errno values from Linux that Zephyr uses are
available.

Signed-off-by: Keith Packard <keithp@keithp.com>

lib/libc/picolibc/CMakeLists.txt

@@ -3,6 +3,10 @@
 zephyr_library()
 zephyr_library_sources(libc-hooks.c)
 
+# define __LINUX_ERRNO_EXTENSIONS__ so we get errno defines like -ESHUTDOWN
+# used by the network stack
+zephyr_compile_definitions(__LINUX_ERRNO_EXTENSIONS__)
+
 if(NOT CONFIG_PICOLIBC_USE_MODULE)
 
   # Use picolibc provided with the toolchain