Whoops, last message bounced from the list due to a bug in the very email client in question (although it went through to Aaron). Grabbed a patch from their list to address this for now, attached; the diff to go.port.mk is also reproduced below.
diff --git a/lang/go/go.port.mk b/lang/go/go.port.mk
index 983c3990706..21bccbd7053 100644
--- a/lang/go/go.port.mk
+++ b/lang/go/go.port.mk
@@ -67,7 +67,7 @@ MODGO_SETUP_WORKSPACE = mkdir -p ${WRKSRC:H}; mv
${MODGO_SUBDIR} ${WRKSRC};
CATEGORIES += lang/go
MODGO_BUILD_TARGET = ${MODGO_BUILD_CMD} ${ALL_TARGET}
-MODGO_FLAGS += -v -p ${MAKE_JOBS}
+MODGO_FLAGS += -v -p=${MAKE_JOBS}
.if empty(DEBUG)
# by default omit symbol table, debug information and DWARF symbol table
aerc.tgz
Description: GNU Zip compressed data
