Makefile: consider GOHOSTFLAGS for ENV variable and descriptions target

When building with the Yocto go-mod class, the -modcacherw flag appended
to GOHOSTFLAGS must be considered in all build steps to make the go
cache writeable (deletable).

Author: sephalon

Makefile

@@ -32,11 +32,38 @@ $(warning $(RED)run command via tools/syz-env for best compatibility, see:$(RESE
 $(warning $(RED)https://github.com/google/syzkaller/blob/master/docs/contributing.md#using-syz-env$(RESET))
 endif
 
+GITREV=$(shell git rev-parse HEAD)
+ifeq ("$(shell git diff --shortstat)", "")
+	REV=$(GITREV)
+else
+	REV=$(GITREV)+
+endif
+GITREVDATE=$(shell git log -n 1 --format="%cd" --date=format:%Y%m%d-%H%M%S)
+
+# Don't generate symbol table and DWARF debug info.
+# Reduces build time and binary sizes considerably.
+# That's only needed if you use gdb or nm.
+# If you need that, build manually with DEBUG=true env.
+GLFLAGS :=
+GGFLAGS :=
+ifeq ("$(DEBUG)", "true")
+	GGFLAGS := -gcflags="all=-N -l"
+else
+	GLFLAGS := -s -w
+endif
+GOFLAGS := -ldflags="$(GLFLAGS) -X github.com/google/syzkaller/prog.GitRevision=$(REV) -X github.com/google/syzkaller/prog.gitRevisionDate=$(GITREVDATE)" $(GGFLAGS)
+ifneq ("$(GOTAGS)", "")
+	GOFLAGS += " -tags=$(GOTAGS)"
+endif
+
+GOHOSTFLAGS ?= $(GOFLAGS)
+GOTARGETFLAGS ?= $(GOFLAGS)
+
 ENV := $(subst \n,$(newline),$(shell CI=$(CI)\
 	SOURCEDIR=$(SOURCEDIR) HOSTOS=$(HOSTOS) HOSTARCH=$(HOSTARCH) \
 	TARGETOS=$(TARGETOS) TARGETARCH=$(TARGETARCH) TARGETVMARCH=$(TARGETVMARCH) \
 	SYZ_CLANG=$(SYZ_CLANG) \
-	go run tools/syz-make/make.go))
+	go run $(GOHOSTFLAGS) tools/syz-make/make.go))
 # Uncomment in case of emergency.
 # $(info $(ENV))
 $(eval $(ENV))
@@ -61,33 +88,6 @@ TARGETGOARCH := $(TARGETVMARCH)
 export GO111MODULE=on
 export GOBIN=$(shell pwd -P)/bin
 
-GITREV=$(shell git rev-parse HEAD)
-ifeq ("$(shell git diff --shortstat)", "")
-	REV=$(GITREV)
-else
-	REV=$(GITREV)+
-endif
-GITREVDATE=$(shell git log -n 1 --format="%cd" --date=format:%Y%m%d-%H%M%S)
-
-# Don't generate symbol table and DWARF debug info.
-# Reduces build time and binary sizes considerably.
-# That's only needed if you use gdb or nm.
-# If you need that, build manually with DEBUG=true env.
-GLFLAGS :=
-GGFLAGS :=
-ifeq ("$(DEBUG)", "true")
-	GGFLAGS := -gcflags="all=-N -l"
-else
-	GLFLAGS := -s -w
-endif
-GOFLAGS := -ldflags="$(GLFLAGS) -X github.com/google/syzkaller/prog.GitRevision=$(REV) -X github.com/google/syzkaller/prog.gitRevisionDate=$(GITREVDATE)" $(GGFLAGS)
-ifneq ("$(GOTAGS)", "")
-	GOFLAGS += " -tags=$(GOTAGS)"
-endif
-
-GOHOSTFLAGS ?= $(GOFLAGS)
-GOTARGETFLAGS ?= $(GOFLAGS)
-
 ifeq ("$(TARGETOS)", "test")
 	TARGETGOOS := $(HOSTOS)
 	TARGETGOARCH := $(HOSTARCH)
@@ -150,7 +150,7 @@ endif
 # syz-sysgen generates them all at once, so we can't make each of them an independent target.
 .PHONY: descriptions
 descriptions:
-	go list -f '{{.Stale}}' ./sys/syz-sysgen | grep -q false || go install ./sys/syz-sysgen
+	go list -f '{{.Stale}}' $(GOHOSTFLAGS) ./sys/syz-sysgen | grep -q false || go install $(GOHOSTFLAGS) ./sys/syz-sysgen
 	$(MAKE) .descriptions
 
 .descriptions: sys/*/*.txt sys/*/*.const bin/syz-sysgen