consider enabling flto for release builds on Linux

[ee7]

Currently, it's only enabled for macOS:

nimutils/nimutils/nimscript.nim

Lines 76 to 86 in eed75bb

	when defined(macosx):
	switch("cpu", targetArch)
	switch("passc", "-flto -target " & targetStr)
	switch("passl", "-flto -w -target " & targetStr &
	"-Wl,-object_path_lto,lto.o")
	elif defined(linux):
	if staticLink:
	switch("passc", "-static")
	switch("passl", "-static")
	else:
	discard