[krbdev.mit.edu #8928] [PATCH] Constructor/destructor configure check fails on certain compilers

Sat Jul 18 20:32:54 2020: Request 8928 was acted upon.
 Transaction: Ticket created by [email protected]
       Queue: krb5
     Subject: [PATCH] Constructor/destructor configure check fails on certain compilers
       Owner: Nobody
  Requestors: [email protected]
      Status: new
 Ticket <URL: https://krbdev.mit.edu/rt/Ticket/Display.html?id=8928 >


On recent versions of clang, calling functions without first having
imported their headers is an error. This causes the
constructor/destructor configure check to fail; it doesn't include any
headers, and a function it uses goes undefined. Sample error:

configure:5947: checking for constructor/destructor attribute support
configure:5975: clang -o conftest -g -O2 -fno-common
-Wl,-search_paths_first conftest.c -lresolv  >&5
conftest.c:25:15: error: implicit declaration of function 'unlink' is
invalid in C99 [-Werror,-Wimplicit-function-declaration]
void foo1() { unlink("conftest.1"); }
              ^

Patch:

diff --git a/src/aclocal.m4 b/src/aclocal.m4
index 2394f7e..811e987 100644
--- a/src/aclocal.m4
+++ b/src/aclocal.m4
@@ -1606,7 +1606,8 @@ fi
 a=no
 b=no
 # blindly assume we have 'unlink'...
-AC_TRY_RUN([void foo1() __attribute__((constructor));
+AC_TRY_RUN([#include <unistd.h>
+void foo1() __attribute__((constructor));
 void foo1() { unlink("conftest.1"); }
 void foo2() __attribute__((destructor));
 void foo2() { unlink("conftest.2"); }