[Bug c/63782] New: avoid implicit declaration warning for incompatible builtin implicit declaration

[manu at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=63782

            Bug ID: 63782
           Summary: avoid implicit declaration warning for incompatible
                    builtin implicit declaration
           Product: gcc
           Version: unknown
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c
          Assignee: unassigned at gcc dot gnu.org
          Reporter: manu at gcc dot gnu.org

void foo(char *str) {
  strcpy(str, "foo");
}

[t@ws-520 examples]$ clang-3.5 -c -Wall test.c
test.c:2:3: warning: implicitly declaring library function 'strcpy' with
type 'char *(char *, const char *)'
strcpy(str, "foo");
^
test.c:2:3: note: include the header <string.h> or explicitly provide a
declaration for 'strcpy'
1 warning generated.

$ gcc-5 -c -Wall test.c
test.c: In function ‘foo’:
test.c:2:3: warning: implicit declaration of function ‘strcpy’
[-Wimplicit-function-declaration]
   strcpy(str, "foo");
   ^
test.c:2:3: warning: incompatible implicit declaration of built-in function
‘strcpy’
test.c:2:3: note: include ‘<string.h>’ or provide a declaration of ‘strcpy’

The first warning is superfluous if the second is given.

(from a talk by Samsung at LinuxCon Europe:
http://events.linuxfoundation.org/sites/events/files/slides/linuxcon-europe-2014-llvm.pdf)