uml: Check for glibc static libraries

UML statically links against libutil, librt and libpthread. Some hosts do not
necessarily have these libraries installed and we should find out sooner than
later (during the final vmlinux linking stage) about that.

Signed-off-by: Florian Fainelli <f.fainelli@gmail.com>

target/linux/uml/image/Makefile

@@ -22,3 +22,14 @@ define Image/Build
 endef
 
 $(eval $(call BuildImage))
+
+# UML requires linking against several glibc static libraries: libutil, librt
+# and libpthread, check that here. We do not check against libpthread
+# specifically because getting something to build that references a libpthread
+# symbol is pretty involved and Linux distributions package these 3 libraries
+# in the same package.
+
+$(eval $(call TestHostCommand,glibc-static, \
+	Please install a static glibc package. (Missing libutil.a, librt.a or libpthread.a), \
+	echo 'int main(int argc, char **argv) { login(0); timer_gettime(0, 0); return 0; }' | \
+		gcc -include utmp.h -x c -o $(TMP_DIR)/a.out - -static -lutil -lrt))