Run `uname -sm` once, don't use python for HOST_OS_EXTRA

This saves 20-50ms for `lunch` (~7-10%), and double that for every build
execution.

Test: Check HOST_OS_EXTRA on Linux & Mac
Change-Id: I863200b2287c8867f40606237895b1d3ad91e1b3
diff --git a/core/config.mk b/core/config.mk
index dbfcc62..7d4581d 100644
--- a/core/config.mk
+++ b/core/config.mk
@@ -71,6 +71,8 @@
 $(error Please remove --color=always from your  $$GREP_OPTIONS)
 endif
 
+UNAME := $(shell uname -sm)
+
 SRC_TARGET_DIR := $(TOPDIR)build/target
 SRC_API_DIR := $(TOPDIR)prebuilts/sdk/api
 SRC_SYSTEM_API_DIR := $(TOPDIR)prebuilts/sdk/system-api
diff --git a/core/envsetup.mk b/core/envsetup.mk
index 46066e3..d17e9e0 100644
--- a/core/envsetup.mk
+++ b/core/envsetup.mk
@@ -97,8 +97,6 @@
 # compiles except for arm/mips, so the HOST is whatever we are
 # running on
 
-UNAME := $(shell uname -sm)
-
 # HOST_OS
 ifneq (,$(findstring Linux,$(UNAME)))
   HOST_OS := linux
@@ -110,7 +108,15 @@
   HOST_OS := darwin
 endif
 
-HOST_OS_EXTRA:=$(shell python -c "import platform; print(platform.platform())")
+HOST_OS_EXTRA := $(shell uname -rsm)
+ifeq ($(HOST_OS),linux)
+  ifneq ($(wildcard /etc/os-release),)
+    HOST_OS_EXTRA += $(shell source /etc/os-release; echo $$PRETTY_NAME)
+  endif
+else ifeq ($(HOST_OS),darwin)
+  HOST_OS_EXTRA += $(shell sw_vers -productVersion)
+endif
+HOST_OS_EXTRA := $(subst $(space),-,$(HOST_OS_EXTRA))
 
 # BUILD_OS is the real host doing the build.
 BUILD_OS := $(HOST_OS)
diff --git a/core/version_defaults.mk b/core/version_defaults.mk
index 5a89fc9..3506fff 100644
--- a/core/version_defaults.mk
+++ b/core/version_defaults.mk
@@ -212,7 +212,7 @@
   BUILD_DATETIME := $(shell date +%s)
 endif
 
-ifneq (,$(findstring Darwin,$(shell uname -sm)))
+ifneq (,$(findstring Darwin,$(UNAME)))
 DATE := date -r $(BUILD_DATETIME)
 else
 DATE := date -d @$(BUILD_DATETIME)