[openwrt/openwrt] u-boot.mk: add LOCALVERSION (explicitly specify OpenWrt build)

[LEDE Commits]

hauke pushed a commit to openwrt/openwrt.git, branch openwrt-21.02:
https://git.openwrt.org/f1e1daa6e8c71c2185aa37e737f968e9ad838c50

commit f1e1daa6e8c71c2185aa37e737f968e9ad838c50
Author: Josef Schlehofer <pepe.schlehofer at gmail.com>
AuthorDate: Mon Feb 21 18:55:15 2022 +0100

    u-boot.mk: add LOCALVERSION (explicitly specify OpenWrt build)
    
    For debugging purposes, we need to know if users are using modified
    U-boot versions or not. Currently, the U-boot version is somehow
    stripped. This is a little bit problematic when there are
    backported/wip/to-upstream patches.
    
    To make it more confusing, there was (before this commit) two U-boot
    versioning. U-boot compiled by OpenWrt build bots are missing ``Build:``
    This is also the case when the U-boot is compiled locally.
    
    Example:
    ```
    U-Boot SPL 2022.01 (Jan 27 2022 - 00:24:34 +0000)
    U-Boot 2022.01 (Jan 27 2022 - 00:24:34 +0000)
    ```
    
    On the other hand, if you run full build, you can at least see, where it
    was compiled. Notice added ``Build:``.
    
    Example:
    ```
    U-Boot 2022.01 (Jan 27 2022 - 00:24:34 +0000), Build: jenkins-turris-os-packages-burstlab-omnia-216
    ```
    
    In both cases, it is not clear to U-boot developers if it is an unmodified
    build. This is also caused that there is a missing ``.git`` file from
    U-boot folder, and so there is no history. It leads to that it can not
    contain suffix ``-dirty`` (uncommitted modifications) or even something
    else like number of commits, etc. [1]
    
    When U-boot is compiled as it should be, the version should look like
    this: ``U-Boot 2022.04-rc1-01173-g278195ea1f (Feb 11 2022 - 14:46:50 +0100)``
    The date is not changed daily when there are new OpenWrt builds.
    
    This commit adds OpenWrt specific version, which could be verified by
    using strings.
    
    ```
    $ strings bin/targets/mvebu/cortexa9/u-boot-omnia/u-boot-spl.kwb | grep -E "OpenWrt*"
    U-Boot SPL 2022.01-OpenWrt-r18942+54-cbfce92367 (Feb 21 2022 - 13:17:34 +0000)
    arm-openwrt-linux-muslgnueabi-gcc (OpenWrt GCC 11.2.0 r18942+54-cbfce92367) 11.2.0
    2022.01-OpenWrt-r18942+54-cbfce92367
    U-Boot 2022.01-OpenWrt-r18942+54-cbfce92367 (Feb 21 2022 - 13:17:34 +0000)
    ```
    
    [1] https://u-boot.readthedocs.io/en/latest/develop/version.html
    
    Reported-by: Pali Rohár <pali at kernel.org>
    Suggested-by: Karel Kočí <karel.koci at nic.cz>
    [rebased for OpenWrt 21.02]
    Signed-off-by: Josef Schlehofer <pepe.schlehofer at gmail.com>
    (cherry picked from commit d6aa9d9e071d9f23ed26f5142991bc66aefe20f5)
---
 include/u-boot.mk | 1 +
 1 file changed, 1 insertion(+)

diff --git a/include/u-boot.mk b/include/u-boot.mk
index ec9fb15b6c..a3dc540ebe 100644
--- a/include/u-boot.mk
+++ b/include/u-boot.mk
@@ -44,6 +44,7 @@ TARGET_DEP = TARGET_$(BUILD_TARGET)$(if $(BUILD_SUBTARGET),_$(BUILD_SUBTARGET))
 UBOOT_MAKE_FLAGS = \
 	HOSTCC="$(HOSTCC)" \
 	HOSTCFLAGS="$(HOST_CFLAGS) $(HOST_CPPFLAGS) -std=gnu11" \
+	LOCALVERSION="-OpenWrt-$(REVISION)" \
 	HOSTLDFLAGS="$(HOST_LDFLAGS)"
 
 define Build/U-Boot/Target