Add in something the builder can override to augment the GO builds

I've been looking at reasons packagers are not building the Go binaries
and found this with respect to RPMs:

  rpm-software-management/rpm#367

There has been no easy way to inject the otherwise unneeded workaround:
-ldflags=-linkmode=external for building (which, strangely, generates
some sort of warning and gratuitously links glibc to an otherwise
static build), but seems to work.

Until RPM supports Go's native '.note.go.buildid', and RPM requires
'.note.gnu.build-id' on binaries, I guess this can work around it:

   GO_BUILD_FLAGS='-ldflags=-linkmode=external'

Signed-off-by: Andrew G. Morgan <morgan@kernel.org>

Make.Rules

@@ -129,7 +129,7 @@ ifeq ($(GOLANG),yes)
 GOROOT ?= $(shell $(GO) env GOROOT)
 GOCGO ?= $(shell if [ "$(shell $(GO) env CGO_ENABLED)" = 1 ]; then echo yes ; else echo no ; fi)
 GOOSARCH ?= $(shell $(GO) env GOHOSTOS)_$(shell $(GO) env GOHOSTARCH)
-CGO_REQUIRED=$(shell $(topdir)/go/cgo-required.sh $(GO))
+CGO_REQUIRED := $(shell $(topdir)/go/cgo-required.sh $(GO))
 ifeq ($(CGO_REQUIRED),1)
 # Strictly speaking go1.15 doesn't need this, but 1.16 is when the
 # real golang support arrives for non-cgo support, so drop the last
@@ -138,6 +138,7 @@ CGO_LDFLAGS_ALLOW := CGO_LDFLAGS_ALLOW="-Wl,-?-wrap[=,][^-.@][^,]*"
 endif
 CGO_CFLAGS := -I$(topdir)/libcap/include
 CGO_LDFLAGS := -L$(topdir)/libcap
+GO_BUILD_FLAGS :=
 endif
 endif
 

go/Makefile

@@ -55,44 +55,44 @@ CAPGOPACKAGE: vendor/$(IMPORTDIR)/cap ../cap/*.go good-names.go $(PSXGOPACKAGE)
 # Compiles something with this package to compare it to libcap. This
 # tests more when run under sudotest (see ../progs/quicktest.sh for that).
 compare-cap: compare-cap.go CAPGOPACKAGE
-	CC="$(CC)" $(CGO_LDFLAGS_ALLOW) CGO_CFLAGS="$(CGO_CFLAGS)" CGO_LDFLAGS="$(CGO_LDFLAGS)" $(GO) build -mod=vendor $<
+	CC="$(CC)" $(CGO_LDFLAGS_ALLOW) CGO_CFLAGS="$(CGO_CFLAGS)" CGO_LDFLAGS="$(CGO_LDFLAGS)" $(GO) build $(GO_BUILD_FLAGS) -mod=vendor $<
 
 web: ../goapps/web/web.go CAPGOPACKAGE
-	CC="$(CC)" CGO_ENABLED="$(CGO_REQUIRED)" $(CGO_LDFLAGS_ALLOW) $(GO) build -mod=vendor -o $@ $<
+	CC="$(CC)" CGO_ENABLED="$(CGO_REQUIRED)" $(CGO_LDFLAGS_ALLOW) $(GO) build $(GO_BUILD_FLAGS) -mod=vendor -o $@ $<
 ifeq ($(RAISE_GO_FILECAP),yes)
 	$(MAKE) -C ../progs setcap
 	$(SUDO) ../progs/setcap cap_setpcap,cap_net_bind_service=p web
 	@echo "NOTE: RAISED cap_setpcap,cap_net_bind_service ON web binary"
 endif
 
 setid: ../goapps/setid/setid.go CAPGOPACKAGE PSXGOPACKAGE
-	CC="$(CC)" CGO_ENABLED="$(CGO_REQUIRED)" $(CGO_LDFLAGS_ALLOW) $(GO) build -mod=vendor -o $@ $<
+	CC="$(CC)" CGO_ENABLED="$(CGO_REQUIRED)" $(CGO_LDFLAGS_ALLOW) $(GO) build $(GO_BUILD_FLAGS) -mod=vendor -o $@ $<
 
 gowns: ../goapps/gowns/gowns.go CAPGOPACKAGE
-	CC="$(CC)" CGO_ENABLED="$(CGO_REQUIRED)" $(CGO_LDFLAGS_ALLOW) $(GO) build -mod=vendor -o $@ $<
+	CC="$(CC)" CGO_ENABLED="$(CGO_REQUIRED)" $(CGO_LDFLAGS_ALLOW) $(GO) build $(GO_BUILD_FLAGS) -mod=vendor -o $@ $<
 
 captree: ../goapps/captree/captree.go CAPGOPACKAGE
-	CC="$(CC)" CGO_ENABLED="$(CGO_REQUIRED)" $(CGO_LDFLAGS_ALLOW) $(GO) build -mod=vendor -o $@ $<
+	CC="$(CC)" CGO_ENABLED="$(CGO_REQUIRED)" $(CGO_LDFLAGS_ALLOW) $(GO) build $(GO_BUILD_FLAGS) -mod=vendor -o $@ $<
 
 ok: ok.go
-	CC="$(CC)" CGO_ENABLED=0 $(GO) build -mod=vendor $<
+	CC="$(CC)" CGO_ENABLED=0 $(GO) build $(GO_BUILD_FLAGS) -mod=vendor $<
 
 try-launching: try-launching.go CAPGOPACKAGE ok
-	CC="$(CC)" CGO_ENABLED="$(CGO_REQUIRED)" $(CGO_LDFLAGS_ALLOW) $(GO) build -mod=vendor $<
+	CC="$(CC)" CGO_ENABLED="$(CGO_REQUIRED)" $(CGO_LDFLAGS_ALLOW) $(GO) build $(GO_BUILD_FLAGS) -mod=vendor $<
 ifeq ($(CGO_REQUIRED),0)
-	CC="$(CC)" CGO_ENABLED="1" $(CGO_LDFLAGS_ALLOW) $(GO) build -mod=vendor -o $@-cgo $<
+	CC="$(CC)" CGO_ENABLED="1" $(CGO_LDFLAGS_ALLOW) $(GO) build $(GO_BUILD_FLAGS) -mod=vendor -o $@-cgo $<
 endif
 
 psx-signals: psx-signals.go PSXGOPACKAGE
-	CC="$(CC)" CGO_ENABLED="$(CGO_REQUIRED)" $(CGO_LDFLAGS_ALLOW) CGO_CFLAGS="$(CGO_CFLAGS)" CGO_LDFLAGS="$(CGO_LDFLAGS)" $(GO) build -mod=vendor $<
+	CC="$(CC)" CGO_ENABLED="$(CGO_REQUIRED)" $(CGO_LDFLAGS_ALLOW) CGO_CFLAGS="$(CGO_CFLAGS)" CGO_LDFLAGS="$(CGO_LDFLAGS)" $(GO) build $(GO_BUILD_FLAGS) -mod=vendor $<
 
 ifeq ($(CGO_REQUIRED),0)
 psx-signals-cgo: psx-signals.go PSXGOPACKAGE
-	CC="$(CC)" CGO_ENABLED="1" $(CGO_LDFLAGS_ALLOW) CGO_CFLAGS="$(CGO_CFLAGS)" CGO_LDFLAGS="$(CGO_LDFLAGS)" $(GO) build -mod=vendor -o $@ $<
+	CC="$(CC)" CGO_ENABLED="1" $(CGO_LDFLAGS_ALLOW) CGO_CFLAGS="$(CGO_CFLAGS)" CGO_LDFLAGS="$(CGO_LDFLAGS)" $(GO) build $(GO_BUILD_FLAGS) -mod=vendor -o $@ $<
 endif
 
 b210613: b210613.go CAPGOPACKAGE
-	CC="$(CC)" CGO_ENABLED="$(CGO_REQUIRED)" $(CGO_LDFLAGS_ALLOW) CGO_CFLAGS="$(CGO_CFLAGS)" CGO_LDFLAGS="$(CGO_LDFLAGS)" $(GO) build -mod=vendor $<
+	CC="$(CC)" CGO_ENABLED="$(CGO_REQUIRED)" $(CGO_LDFLAGS_ALLOW) CGO_CFLAGS="$(CGO_CFLAGS)" CGO_LDFLAGS="$(CGO_LDFLAGS)" $(GO) build $(GO_BUILD_FLAGS) -mod=vendor $<
 
 test: setid gowns captree $(TESTS)
 	CC="$(CC)" CGO_ENABLED="$(CGO_REQUIRED)" $(CGO_LDFLAGS_ALLOW) $(GO) test -mod=vendor $(IMPORTDIR)/psx