Fix --enable-invariants on FreeBSD

The make symbols were never getting forwarded to the correct make
subprocess.  As far as I can tell, this has never worked.  Either that,
or something has changed in the behavior of make.

Reviewed-by: Brian Behlendorf <behlendorf1@llnl.gov>
Signed-off-by: Alan Somers <asomers@gmail.com>
Closes openzfs#18131

Author: asomers

module/Makefile.in

@@ -19,8 +19,8 @@ check:
 	cppcheck cppcheck-Linux cppcheck-FreeBSD
 
 # For FreeBSD, use debug options from ./configure if not overridden.
-export WITH_DEBUG ?= @WITH_DEBUG@
-export WITH_INVARIANTS ?= @WITH_INVARIANTS@
+WITH_DEBUG ?= @WITH_DEBUG@
+WITH_INVARIANTS ?= @WITH_INVARIANTS@
 
 # Filter out options that FreeBSD make doesn't understand
 getflags = ( \
@@ -43,6 +43,7 @@ done; \
 echo $$fmakeflags \
 )
 FMAKEFLAGS = -C @abs_srcdir@ -f Makefile.bsd $(shell $(getflags))
+FMAKEFLAGS += WITH_DEBUG=$(WITH_DEBUG) WITH_INVARIANTS=$(WITH_INVARIANTS)
 
 ifneq (@abs_srcdir@,@abs_builddir@)
 FMAKEFLAGS += MAKEOBJDIR=@abs_builddir@