[XEN PATCH for-4.17] tools: Workaround wrong use of tools/Rules.mk by qemu-trad

[Anthony PERARD <anthony.perard@xxxxxxxxxx>]

qemu-trad build system, when built from xen.git, will make use of
Rules.mk (setup via qemu-trad.git/xen-setup). This mean that changes
to Rules.mk will have an impact our ability to build qemu-trad.

Recent commit e4f5949c4466 ("tools: Add -Werror by default to all
tools/") have added "-Werror" to the CFLAGS and qemu-trad start to use
it. But this fails and there's lots of warning that are now turned
into error.

We should teach qemu-trad and xen.git to not have to use Rules.mk when
building qemu-trad, but for now, avoid adding -Werror to CFLAGS when
building qemu-trad.

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

Notes:
    for 4.17:
        - fix the build, as detected by the push-gate

 tools/Makefile | 1 +
 tools/Rules.mk | 3 +++
 2 files changed, 4 insertions(+)

diff --git a/tools/Makefile b/tools/Makefile
index 0c1d8b64a4..9e28027835 100644
--- a/tools/Makefile
+++ b/tools/Makefile
@@ -159,6 +159,7 @@ qemu-traditional-recurse = \
        set -e; \
                $(buildmakevars2shellvars); \
                export CONFIG_BLKTAP1=n; \
+               export BUILDING_QEMU_TRAD=y; \
                cd qemu-xen-traditional-dir; \
                $(1)
 
diff --git a/tools/Rules.mk b/tools/Rules.mk
index 34d495fff7..6e135387bd 100644
--- a/tools/Rules.mk
+++ b/tools/Rules.mk
@@ -141,9 +141,12 @@ endif
 
 CFLAGS_libxenlight += $(CFLAGS_libxenctrl)
 
+# Don't add -Werror if we are used by qemu-trad build system.
+ifndef BUILDING_QEMU_TRAD
 ifeq ($(CONFIG_WERROR),y)
 CFLAGS += -Werror
 endif
+endif
 
 ifeq ($(debug),y)
 # Use -Og if available, -O0 otherwise
-- 
Anthony PERARD