Add an UNDEFINED_VERSION option

When enabled (current default) link with --undefined-version to allow
symbol maps to contain symbols not defined by libraries.  When disabled,
link with --no-undefined-version to disallow these bugs.

WITHOUT_UNDEFINED_VERSION is currently broken.  Once it is fixed it
should be made the default and this option should likely be removed.

Reviewed by:	dim, emaste
Differential Revision:	https://reviews.freebsd.org/D44169

share/man/man5/src.conf.5

@@ -1,5 +1,5 @@
 .\" DO NOT EDIT-- this file is @generated by tools/build/options/makeman.
-.Dd February 17, 2024
+.Dd March 1, 2024
 .Dt SRC.CONF 5
 .Os
 .Sh NAME
@@ -1726,6 +1726,9 @@ and that the runtime support library is available
 Do not build
 .Xr unbound 8
 and related programs.
+.It Va WITHOUT_UNDEFINED_VERSION
+Link libraries with --no-undefined-version to ensure all symbols are
+provided.
 .It Va WITHOUT_UNIFIED_OBJDIR
 Use the historical object directory format for
 .Xr build 7

share/mk/bsd.lib.mk

@@ -260,10 +260,12 @@ SHLIB_NAME_FULL=${SHLIB_NAME}
 ${SHLIB_NAME_FULL}:	${VERSION_MAP}
 LDFLAGS+=	-Wl,--version-script=${VERSION_MAP}
 
-# lld >= 16 turned on --no-undefined-version by default, but we have several
-# symbols in our version maps that may or may not exist, depending on
-# compile-time defines.
-.if ${LINKER_TYPE} == "lld" && ${LINKER_VERSION} >= 160000
+# Ideally we'd always enable --no-undefined-version (default for lld >= 16),
+# but we have several symbols in our version maps that may or may not exist,
+# depending on compile-time defines and that needs to be handled first.
+.if ${MK_UNDEFINED_VERSION} == "no"
+LDFLAGS+=	-Wl,--no-undefined-version
+.else
 LDFLAGS+=	-Wl,--undefined-version
 .endif
 .endif

share/mk/bsd.opts.mk

@@ -68,6 +68,7 @@ __DEFAULT_YES_OPTIONS = \
     SSP \
     TESTS \
     TOOLCHAIN \
+    UNDEFINED_VERSION \
     WARNS \
     WERROR
 

tools/build/options/WITHOUT_UNDEFINED_VERSION

@@ -0,0 +1,2 @@
+Link libraries with --no-undefined-version to ensure all symbols are
+provided.