qemu: correct kernel headers check when major numbers differ

commit f7add51c39 (qemu: add host/target Linux version check) added a
version check between the host kernel version and the version of kernel
headers used by the toolchain, but the logic would fail unless BOTH major
and minor versions were >=, which isn't true for E.G. host kernel = 3.2 and
toolchain 2.6.x.

Instead calculate a single version number (as major << 8 + minor) and
compare that.

Signed-off-by: Peter Korsgaard <peter@korsgaard.com>

package/qemu/qemu.mk

@@ -65,12 +65,10 @@ ifneq ($(HOST_QEMU_HOST_SYSTEM_TYPE),Linux)
 $(error "qemu-user can only be used on Linux hosts")
 endif
 
-HOST_QEMU_HOST_SYSTEM_VERSION_MAJOR = $(shell uname -r | cut -f1 -d'.')
-HOST_QEMU_HOST_SYSTEM_VERSION_MINOR = $(shell uname -r | cut -f2 -d'.')
-HOST_QEMU_TARGET_SYSTEM_VERSION_MAJOR = $(shell echo $(BR2_TOOLCHAIN_HEADERS_AT_LEAST) | cut -f1 -d'.')
-HOST_QEMU_TARGET_SYSTEM_VERSION_MINOR = $(shell echo $(BR2_TOOLCHAIN_HEADERS_AT_LEAST) | cut -f2 -d'.')
-HOST_QEMU_COMPARE_VERSION_MAJOR = $(shell test $(HOST_QEMU_HOST_SYSTEM_VERSION_MAJOR) -ge $(HOST_QEMU_TARGET_SYSTEM_VERSION_MAJOR) && echo OK)
-HOST_QEMU_COMPARE_VERSION_MINOR = $(shell test $(HOST_QEMU_HOST_SYSTEM_VERSION_MINOR) -ge $(HOST_QEMU_TARGET_SYSTEM_VERSION_MINOR) && echo OK)
+# kernel version as major*256 + minor
+HOST_QEMU_HOST_SYSTEM_VERSION = $(shell uname -r | awk -F. '{ print $$1 * 256 + $$2 }')
+HOST_QEMU_TARGET_SYSTEM_VERSION = $(shell echo $(BR2_TOOLCHAIN_HEADERS_AT_LEAST) | awk -F. '{ print $$1 * 256 + $$2 }')
+HOST_QEMU_COMPARE_VERSION = $(shell test $(HOST_QEMU_HOST_SYSTEM_VERSION) -ge $(HOST_QEMU_TARGET_SYSTEM_VERSION) && echo OK)
 
 #
 # The principle of qemu-user is that it emulates the instructions of
@@ -82,7 +80,7 @@ HOST_QEMU_COMPARE_VERSION_MINOR = $(shell test $(HOST_QEMU_HOST_SYSTEM_VERSION_M
 # built with kernel headers that are older or the same as the kernel
 # version running on the host machine.
 #
-ifneq ($(HOST_QEMU_COMPARE_VERSION_MAJOR)$(HOST_QEMU_COMPARE_VERSION_MINOR),OKOK)
+ifneq ($(HOST_QEMU_COMPARE_VERSION),OK)
 $(error "Refusing to build qemu-user: target Linux version newer than host's.")
 endif
 endif