[XEN PATCH v2] build: detect compiler change to rerun kconfig

[Anthony PERARD <anthony.perard@xxxxxxxxxx>]

This simple comment allows to detect when $(CC) changes version.
Kconfig will be rerun in this case. (Rerun is forced by
include/config/auto.conf.cmd which detects changes of CC_VERSION_TEXT
value).

Signed-off-by: Anthony PERARD <anthony.perard@xxxxxxxxxx>
---

Technically, it was acked by Andrew:
    
https://lore.kernel.org/xen-devel/20200326135621.687685-1-anthony.perard@xxxxxxxxxx/t/#ma1171775b9938bcdffc80b2fcb8d2a883cd3e32a

v2:
- s/upgrade/change/ in subject and in the comment in the Makefile
- Fix path in commit description
---
 xen/Kconfig  | 2 ++
 xen/Makefile | 4 ++++
 2 files changed, 6 insertions(+)

diff --git a/xen/Kconfig b/xen/Kconfig
index 134e6e68ad..756c7842e9 100644
--- a/xen/Kconfig
+++ b/xen/Kconfig
@@ -4,6 +4,8 @@
 #
 mainmenu "Xen/$(SRCARCH) $(XEN_FULLVERSION) Configuration"
 
+comment "Compiler: $(CC_VERSION_TEXT)"
+
 source "scripts/Kconfig.include"
 
 config BROKEN
diff --git a/xen/Makefile b/xen/Makefile
index 2710d7327e..12c6891a79 100644
--- a/xen/Makefile
+++ b/xen/Makefile
@@ -326,6 +326,10 @@ ifdef building_out_of_srctree
        { echo "# this is build directory, ignore it"; echo "*"; } > .gitignore
 endif
 
+# CC_VERSION_TEXT is referenced from Kconfig (so it needs export),
+# and from include/config/auto.conf.cmd to detect the compiler change.
+export CC_VERSION_TEXT := $(shell $(CC) --version 2>/dev/null | head -n 1)
+
 ifeq ($(config-build),y)
 # ===========================================================================
 # *config targets only - make sure prerequisites are updated, and descend
-- 
Anthony PERARD