picolibc: Remove _POSIX_C_SOURCE define

Don't ask picolibc to expose the full POSIX API by default, instead have it
only define the Zephyr API.

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

Author: keith-packard

lib/libc/picolibc/CMakeLists.txt

@@ -12,7 +12,6 @@ if(NOT CONFIG_PICOLIBC_USE_MODULE)
   # Use picolibc provided with the toolchain
 
   zephyr_compile_options(--specs=picolibc.specs)
-  zephyr_compile_definitions(_POSIX_C_SOURCE=200809)
   zephyr_libc_link_libraries(-T/dev/null --specs=picolibc.specs c -lgcc)
   if(CONFIG_PICOLIBC_IO_FLOAT)
     zephyr_compile_definitions(PICOLIBC_DOUBLE_PRINTF_SCANF)