Index: tools/build/Makefile
===================================================================
--- tools/build/Makefile
+++ tools/build/Makefile
@@ -153,6 +153,15 @@
 
 .if ${.MAKE.OS} != "FreeBSD"
 .PATH: ${.CURDIR}/cross-build
+
+# Needed by our sys/types.h wrapper
+SYSINCS+=	${SRCTOP}/sys/sys/bitcount.h
+
+# macOS's bitstring lacks FreeBSD-specific additions used by makefs's ZFS code
+# and Linux doesn't have it at all.
+INCS+=	${SRCTOP}/include/bitstring.h
+SYSINCS+=	${SRCTOP}/sys/sys/bitstring.h
+
 # dbopen() behaves differently on Linux and FreeBSD so we ensure that we
 # bootstrap the FreeBSD db code. The cross-build headers #define dbopen() to
 # __freebsd_dbopen() so that we don't ever use the host version
Index: tools/build/cross-build/include/common/sys/types.h
===================================================================
--- tools/build/cross-build/include/common/sys/types.h
+++ tools/build/cross-build/include/common/sys/types.h
@@ -68,4 +68,8 @@
 struct cap_rights;
 
 typedef struct cap_rights cap_rights_t;
+
+/* Needed for bitstring */
+#include <sys/bitcount.h>
+
 #endif