[libc++] Check for _newlib_version.h in addition to picolibc.h

Fixes #152763.

#131921 added some code to
pull in a definition of _NEWLIB_VERSION if it exists. It does this
by checking __has_include(<picolibc.h>) and including it if so.
However, this does not work for systems that have newlib rather
than picolibc. With this change, we check for either picolibc.h
or _newlib_version.h, which works for both newlib and picolibc.

Author: inglorion

libcxx/include/__configuration/platform.h

@@ -45,7 +45,9 @@
 // This is required in order for _NEWLIB_VERSION to be defined in places where we use it.
 // TODO: We shouldn't be including arbitrarily-named headers from libc++ since this can break valid
 //       user code. Move code paths that need _NEWLIB_VERSION to another customization mechanism.
-#if __has_include(<picolibc.h>)
+#if __has_include(<_newlib_version.h>)
+#  include <_newlib_version.h>
+#elif __has_include(<picolibc.h>)
 #  include <picolibc.h>
 #endif