[git commit] build system: fix broken CONFIG_SYSROOT handling

[Denys Vlasenko]

commit: http://git.busybox.net/busybox/commit/?id=39c2cb2e93e2acc75a5eb6dd91d81f79c787acd5
branch: http://git.busybox.net/busybox/commit/?id=refs/heads/master

Signed-off-by: Denys Vlasenko <vda.linux at googlemail.com>
---
 Makefile.flags |    4 +++-
 1 files changed, 3 insertions(+), 1 deletions(-)

diff --git a/Makefile.flags b/Makefile.flags
index 68dfa57..92aae6f 100644
--- a/Makefile.flags
+++ b/Makefile.flags
@@ -104,7 +104,9 @@ else
 LDLIBS += m
 endif
 
-ifneq ($(CONFIG_SYSROOT),)
+# Note: both "" (string consisting of two quote chars) and empty string
+# are possible, and should be skipped below.
+ifneq ($(subst "",,$(CONFIG_SYSROOT)),)
 CFLAGS += --sysroot=$(CONFIG_SYSROOT)
 export SYSROOT=$(CONFIG_SYSROOT)
 endif