build: nmk -- Filter out -Wl flags from linking builtin targets

Tycho reported that Debian uses custom LDFLAGS to
build criu, this flag get propagated into built-in
targets where we use $(LD) instead causing build
procedure to interrupt

|  LINK     arch/x86/syscalls.built-in.o
| ld: unrecognized option '-Wl,-Bsymbolic-functions'
| ld: use the --help option for usage information
| /«PKGBUILDDIR»/scripts/nmk/scripts/build.mk:141: recipe for target 'arch/x86/syscalls.built-in.o' failed

Lets make maintainers life easier and filter
out the flags we know never accepted by $(LD).
Reported-by: Tycho Andersen <tycho.andersen@canonical.com>
Tested-by: Tycho Andersen <tycho.andersen@canonical.com>
Signed-off-by: Cyrill Gorcunov <gorcunov@openvz.org>
Reviewed-by: Dmitry Safonov <dsafonov@virtuozzo.com>
Signed-off-by: Pavel Emelyanov <xemul@virtuozzo.com>

scripts/nmk/scripts/build.mk

@@ -24,6 +24,15 @@ ifndef obj
         $(error obj is undefined)
 endif
 
+#
+# Filter out any -Wl,XXX option: some of build farms
+# assumes that we're using $(CC) for building built-in
+# targets (and they have all rights to). But we're
+# using $(LD) directly instead so filter out -Wl
+# flags to make maintainer's life easier.
+LDFLAGS-MASK	:= -Wl,%
+LDFLAGS		:= $(filter-out $(LDFLAGS-MASK),$(LDFLAGS))
+
 #
 # Accumulate common flags.
 define nmk-ccflags