[llvm-bugs] [Bug 34557] New: Builtin prototypes are implicitly defined

[via llvm-bugs]

https://bugs.llvm.org/show_bug.cgi?id=34557

            Bug ID: 34557
           Summary: Builtin prototypes are implicitly defined
           Product: clang
           Version: unspecified
          Hardware: PC
                OS: All
            Status: NEW
          Severity: enhancement
          Priority: P
         Component: Frontend
          Assignee: unassignedclangbugs at nondot.org
          Reporter: joerg at NetBSD.org
                CC: llvm-bugs at lists.llvm.org

A common way to do autoconf-style tests for declarations in headers uses the
following approach:

int main(void) { (void)strlcpy; return 0; }

This should fail with unknown identifier errors, but currently passes with a
implicit prototype warning for GNUish language modes (i.e. gnu89, gnu99 etc).
It fails for "unknown" identifiers like strlcpy2. This is a pretty bad error as
it can lead to incorrect autodetection of system headers.

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