Resolve conflicts for functions introduced in Android API level 23. * lib/string.in.h (mempcpy): Consider REPLACE_MEMPCPY. Disable _GL_CXXALIASWARN invocation on non-glibc systems. * m4/string_h.m4 (gl_STRING_H_DEFAULTS): Initialize REPLACE_MEMPCPY. * modules/string (Makefile.am): Substitute REPLACE_MEMPCPY. * m4/mempcpy.m4 (gl_FUNC_STPCPY): Conditionally set REPLACE_MEMPCPY. * modules/mempcpy (configure.ac): Consider REPLACE_MEMPCPY.