Without this definition, the errno definition for newlib
isn't recognized as such, and these tests fail for newlib
targets:

FAIL: gcc.dg/analyzer/call-summaries-errno.c  (test for warnings, line 16)
FAIL: gcc.dg/analyzer/call-summaries-errno.c (test for excess errors)
FAIL: gcc.dg/analyzer/errno-1.c  (test for warnings, line 20)
FAIL: gcc.dg/analyzer/errno-1.c (test for excess errors)
FAIL: gcc.dg/analyzer/flex-without-call-summaries.c (test for excess errors)
FAIL: gcc.dg/analyzer/isatty-1.c  (test for warnings, line 31)
FAIL: gcc.dg/analyzer/isatty-1.c  (test for warnings, line 35)
FAIL: gcc.dg/analyzer/isatty-1.c  (test for warnings, line 46)
FAIL: gcc.dg/analyzer/isatty-1.c  (test for warnings, line 56)
FAIL: gcc.dg/analyzer/isatty-1.c (test for excess errors)

gcc/analyzer:
	* kf.cc (register_known_functions): Add __errno function for newlib.