Detect version of sed in Makefile (#12319)

* Detect version of sed in Makefile

It's possible to install GNU sed on Darwin or FreeBSD so it's better to
not assume BSD sed on those platforms but to instead perform version
detection for the `GNU` string and only use BSD syntax if absent.

* silence stderr

Co-authored-by: Lauris BH <lauris@nix.lv>
Co-authored-by: techknowlogick <techknowlogick@gitea.io>

Makefile

@@ -21,7 +21,6 @@ IMPORT := code.gitea.io/gitea
 export GO111MODULE=on
 
 GO ?= go
-SED_INPLACE := sed -i
 SHASUM ?= shasum -a 256
 HAS_GO = $(shell hash $(GO) > /dev/null 2>&1 && echo "GO" || echo "NOGO" )
 COMMA := ,
@@ -42,18 +41,16 @@ ifeq ($(HAS_GO), GO)
 	CGO_CFLAGS ?= $(shell $(GO) env CGO_CFLAGS) $(CGO_EXTRA_CFLAGS)
 endif
 
-
 ifeq ($(OS), Windows_NT)
 	EXECUTABLE ?= gitea.exe
 else
 	EXECUTABLE ?= gitea
-	UNAME_S := $(shell uname -s)
-	ifeq ($(UNAME_S),Darwin)
-		SED_INPLACE := sed -i ''
-	endif
-	ifeq ($(UNAME_S),FreeBSD)
-		SED_INPLACE := sed -i ''
-	endif
+endif
+
+ifeq ($(shell sed --version 2>/dev/null | grep -q GNU && echo gnu),gnu)
+	SED_INPLACE := sed -i
+else
+	SED_INPLACE := sed -i ''
 endif
 
 GOFMT ?= gofmt -s