xen: append EXTRA_CFLAGS_XEN_CORE to CFLAGS

Allow a user to supply extra CFLAGS via the EXTRA_CFLAGS_XEN_CORE
environment variable for hypervisor builds. This is not a
configuration that is supported but is only aimed to help support
testing and troubleshooting when you need to make changes.

Signed-off-by: Doug Goldstein <cardoe@cardoe.com>
Reviewed-by: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>
Reviewed-by: Wei Liu <wei.liu2@citrix.com>

INSTALL

@@ -247,6 +247,10 @@ EXTRA_CFLAGS_XEN_TOOLS=
 EXTRA_CFLAGS_QEMU_TRADITIONAL=
 EXTRA_CFLAGS_QEMU_XEN=
 
+Additional CFLAGS may be supplied to the build of the hypervisor by
+using this variable.
+EXTRA_CFLAGS_XEN_CORE=
+
 This variable can be used to use DIR/include and DIR/lib during build.
 This is the same as PREPEND_LIB and PREPEND_INCLUDES. APPEND_LIB and
 APPEND_INCLUDES= will be appended to the CFLAGS/LDFLAGS variable.

xen/Rules.mk

@@ -79,6 +79,8 @@ ALL_OBJS := $(ALL_OBJS-y)
 CFLAGS-y += -MMD -MF $(@D)/.$(@F).d
 
 CFLAGS += $(CFLAGS-y)
+# allow extra CFLAGS externally via EXTRA_CFLAGS_XEN_CORE
+CFLAGS += $(EXTRA_CFLAGS_XEN_CORE)
 
 # Most CFLAGS are safe for assembly files:
 #  -std=gnu{89,99} gets confused by #-prefixed end-of-line comments