wireguard: fix portability issue

Check if the compiler defines __linux__, instead of assuming that the
host OS is the same as the target OS.

Signed-off-by: Felix Fietkau <nbd@nbd.name>

package/network/services/wireguard/patches/100-portability.patch

@@ -0,0 +1,18 @@
+tools: fix portability issue
+
+Check if the compiler defines __linux__, instead of assuming that the
+host OS is the same as the target OS.
+
+Signed-off-by: Felix Fietkau <nbd@nbd.name>
+---
+--- a/src/tools/Makefile
++++ b/src/tools/Makefile
+@@ -39,7 +39,7 @@ CFLAGS += -DRUNSTATEDIR="\"$(RUNSTATEDIR
+ ifeq ($(DEBUG_TOOLS),y)
+ CFLAGS += -g
+ endif
+-ifeq ($(shell uname -s),Linux)
++ifeq ($(strip $(shell echo __linux__ | $(CC) -E - | grep -v '^\#')),1)
+ LIBMNL_CFLAGS := $(shell $(PKG_CONFIG) --cflags libmnl 2>/dev/null)
+ LIBMNL_LDLIBS := $(shell $(PKG_CONFIG) --libs libmnl 2>/dev/null || echo -lmnl)
+ CFLAGS += $(LIBMNL_CFLAGS)