Support musl builds in Make

Rewrite linux_musl to linux when exporting to Make.

Bug: 190084016
Test: m USE_HOST_MUSL=true adb
Change-Id: I48eed5bd7380a07c5106a9b2bd96899fb58f7a7f
diff --git a/android/androidmk.go b/android/androidmk.go
index f032f1b..9853d2c 100644
--- a/android/androidmk.go
+++ b/android/androidmk.go
@@ -571,7 +571,7 @@
 
 	if host {
 		makeOs := amod.Os().String()
-		if amod.Os() == Linux || amod.Os() == LinuxBionic {
+		if amod.Os() == Linux || amod.Os() == LinuxBionic || amod.Os() == LinuxMusl {
 			makeOs = "linux"
 		}
 		a.SetString("LOCAL_MODULE_HOST_OS", makeOs)