I'm currently working on Samba4 port for OpenBSD.

At some point, Samba built system picks up /usr/local/lib as library path that should be always used. It starts using it for tests here (excerpt from bin/config.log):

--------------------------------------------------------
Checking for HAVE_RPCSVC_YP_PROT_H
==>
#define CONFIG_H_IS_FROM_SAMBA 1
#define _SAMBA_BUILD_ 4
#define HAVE_CONFIG_H 1
#define BUILD_SYSTEM "OpenBSD persx201i.gnom.domain 5.3 X201I#46 i386"
#define HAVE_SYS_UTSNAME_H 1
#define SYSTEM_UNAME_SYSNAME "OpenBSD"
#define SYSTEM_UNAME_MACHINE "i386"
#define SYSTEM_UNAME_RELEASE "5.3"
#define SYSTEM_UNAME_VERSION "X201I#46"
#define HAVE_STDIO_H 1
#define HAVE_SIMPLE_C_PROG 1
#define INLINE_MACRO 1
#define _GNU_SOURCE 1
#define _XOPEN_SOURCE_EXTENDED 1
#define HAVE_SYS_TYPES_H 1
#define HAVE_SYS_STAT_H 1
#define HAVE_STDLIB_H 1
#define HAVE_STDDEF_H 1
#define HAVE_MEMORY_H 1
#define HAVE_STRING_H 1
#define HAVE_STRINGS_H 1
#define HAVE_INTTYPES_H 1
#define HAVE_STDINT_H 1
#define HAVE_UNISTD_H 1
#define HAVE_CTYPE_H 1
#define HAVE_STDBOOL_H 1
#define HAVE_STDARG_H 1
#define HAVE_LIMITS_H 1
#define HAVE_ASSERT_H 1
#define HAVE_LARGEFILE 1
#define STDC_HEADERS 1
#define HAVE_SYS_TIME_H 1
#define HAVE_TIME_H 1
#define TIME_WITH_SYS_TIME 1
#define SHLIBEXT "so"
/* #undef WORDS_BIGENDIAN */
#define HAVE_SIGNAL_H 1
/* #undef RETSIGTYPE_INT */
#define RETSIGTYPE void
#define HAVE_FUNCTION_MACRO 1
#define HAVE_VA_COPY 1
#define HAVE__VA_ARGS__MACRO 1
#define HAVE_LIBREPLACE 1
#define LIBREPLACE_NETWORK_CHECKS 1
#define HAVE_LOCALE_H 1
#define HAVE_FCNTL_H 1
#define HAVE_FNMATCH_H 1
#define HAVE_GLOB_H 1
#define HAVE_LANGINFO_H 1
#define HAVE_PWD_H 1
#define HAVE_SYS_DIR_H 1
#define HAVE_SYS_FCNTL_H 1
#define HAVE_SYS_FILIO_H 1
#define HAVE_SYS_IOCTL_H 1
#define HAVE_SYS_IPC_H 1
#define HAVE_SYS_MMAN_H 1
#define HAVE_SYS_RESOURCE_H 1
#define HAVE_SYS_SHM_H 1
#define HAVE_SYS_STATVFS_H 1
#define HAVE_TERMIOS_H 1
#define HAVE_SYS_FILE_H 1
#define HAVE_SYS_WAIT_H 1
#define HAVE_MALLOC_H 1
#define HAVE_GRP_H 1
#define HAVE_SYS_SELECT_H 1
#define HAVE_SETJMP_H 1
#define HAVE_UTIME_H 1
#define HAVE_SYS_SYSLOG_H 1
#define HAVE_SYSLOG_H 1
#define HAVE_SYS_PARAM_H 1
#define HAVE_SYS_SOCKET_H 1
#define HAVE_NETINET_IN_H 1
#define HAVE_NETDB_H 1
#define HAVE_ARPA_INET_H 1
#define HAVE_NETINET_IN_SYSTM_H 1
#define HAVE_NETINET_IP_H 1
#define HAVE_NETINET_TCP_H 1
#define HAVE_SYS_SOCKIO_H 1
#define HAVE_SYS_UN_H 1
#define HAVE_SYS_UIO_H 1
#define HAVE_IFADDRS_H 1
#define HAVE_DIRENT_H 1
#define HAVE_LIBINTL_H 1
#define HAVE_ERRNO_H 1
#define HAVE_GCRYPT_H 1
#define HAVE_GETOPT_H 1
#define HAVE_ICONV_H 1
#define HAVE_SASL_SASL_H 1
#define HAVE_ZLIB_H 1
#define HAVE_SYS_UNISTD_H 1
#define HAVE_RPC_RPC_H 1
#define HAVE_FLOAT_H 1
#define HAVE_RPCSVC_YPCLNT_H 1
#define HAVE_SYS_SYSCTL_H 1
#define HAVE_NETGROUP_H 1
#include <stdio.h>
#include <sys/types.h>
#include <sys/stat.h>
#include <stdlib.h>
#include <stddef.h>
#include <memory.h>
#include <string.h>
#include <strings.h>
#include <inttypes.h>
#include <stdint.h>
#include <unistd.h>
#include <ctype.h>
#include <stdbool.h>
#include <stdarg.h>
#include <rpc/rpc.h>

 int main(void) { ; return 0; }

<==
[1/2] Compiling test.c
['cc', '-O2', '-pipe', '-I/usr/ports/pobj/samba-4.0.4/samba-4.0.4/lib/replace', '-MD', '-Idefault', '-I..', '-Idefault', '-I..', '-I/usr/local/include', '-D_SAMBA_BUILD_=4', '-DHAVE_CONFIG_H=1', '-D_GNU_SOURCE=1', '-D_XOPEN_SOURCE_EXTENDED=1', '../test.c', '-c', '-o', 'default/test_1.o']
[2/2] Linking default/testprog
['cc', 'default/test_1.o', '-o', '/usr/ports/pobj/samba-4.0.4/samba-4.0.4/bin/.conf_check_0/testbuild/default/testprog', '-L/usr/local/lib']
ok

--------------------------------------------------------
Checking for header sys/cdefs.h
==>
...


I do not even know why does it look at /usr/local/include even, because the file being checked lies under /usr/include.

This -L/usr/local/lib breaks build when another (e.g., Samba3) version is installed, because linking is being done with the wrong libraries.

I'm attaching the full config.log.