Fix Static_executable, implement BUILD_HOST_static from Make

Static_executable was still using ModifyProperties, and was otherwise
missing things. Fix all of that up, and implement HostStaticBinaries,
which is the equivalent of BUILD_HOST_static in Make. That will default
host binaries to be static, which is useful for building SDK tools to
run with incompatible C libraries.

Change-Id: I2a62181b5d854b310edc8ae7a6bcbd30b89e7463
diff --git a/common/variable.go b/common/variable.go
index 0b5df07..d67a8b7 100644
--- a/common/variable.go
+++ b/common/variable.go
@@ -85,6 +85,7 @@
 	Brillo                     *bool `json:",omitempty"`
 	Malloc_not_svelte          *bool `json:",omitempty"`
 	Safestack                  *bool `json:",omitempty"`
+	HostStaticBinaries         *bool `json:",omitempty"`
 
 	SanitizeHost   *[]string `json:",omitempty"`
 	SanitizeDevice *[]string `json:",omitempty"`