Resolve conflicts for functions introduced in Android API level 21. * lib/stdlib.in.h (_Exit): Consider REPLACE__EXIT. Disable _GL_CXXALIASWARN invocation on non-glibc systems. (getprogname): Consider REPLACE_GETPROGNAME. Disable _GL_CXXALIASWARN invocation on non-glibc systems. (posix_openpt): Consider REPLACE_POSIX_OPENPT. Disable _GL_CXXALIASWARN invocation on non-glibc systems. * m4/stdlib_h.m4 (gl_STDLIB_H_DEFAULTS): Initialize REPLACE__EXIT, REPLACE_GETPROGNAME, REPLACE_POSIX_OPENPT. * modules/stdlib (Makefile.am): Substitute REPLACE__EXIT, REPLACE_GETPROGNAME, REPLACE_POSIX_OPENPT. * m4/_Exit.m4 (gl_FUNC__EXIT): Conditionally set REPLACE__EXIT. * modules/_Exit (configure.ac): Consider REPLACE__EXIT. * m4/getprogname.m4 (gl_FUNC_GETPROGNAME): Conditionally set REPLACE_GETPROGNAME. * modules/getprogname (configure.ac): Consider REPLACE_GETPROGNAME. * m4/posix_openpt.m4 (gl_FUNC_POSIX_OPENPT): Conditionally set REPLACE_POSIX_OPENPT. * modules/posix_openpt (configure.ac): Consider REPLACE_POSIX_OPENPT.