Support gcc host wrapper.

This change adds support for the gcc host wrapper.
The implementation is verified via comparing to the old
gcc host wrapper in the golden tests.

BUG=chromium:773875
TEST=unit test

Change-Id: I3af98b81dba6d9299183db01e967003be860972c
Reviewed-on: https://chromium-review.googlesource.com/c/chromiumos/third_party/toolchain-utils/+/1710537
Tested-by: Tobias Bosch <tbosch@google.com>
Reviewed-by: George Burgess <gbiv@chromium.org>
diff --git a/compiler_wrapper/compiler_wrapper.go b/compiler_wrapper/compiler_wrapper.go
index b2172c6..521846c 100644
--- a/compiler_wrapper/compiler_wrapper.go
+++ b/compiler_wrapper/compiler_wrapper.go
@@ -130,12 +130,19 @@
 }
 
 func calcGccCommand(builder *commandBuilder) *command {
-	sysroot := processSysrootFlag(builder)
+	sysroot := ""
+	if !builder.cfg.isHostWrapper {
+		sysroot = processSysrootFlag(builder)
+	}
 	builder.addPreUserArgs(builder.cfg.gccFlags...)
-	calcCommonPreUserArgs(builder)
+	if !builder.cfg.isHostWrapper {
+		calcCommonPreUserArgs(builder)
+	}
 	processGccFlags(builder)
-	allowCCache := true
-	processGomaCCacheFlags(sysroot, allowCCache, builder)
+	if !builder.cfg.isHostWrapper {
+		allowCCache := true
+		processGomaCCacheFlags(sysroot, allowCCache, builder)
+	}
 	return builder.build()
 }