`libv4l` requires a `gnu` `std`

[shirok1]

...to use typeof

diff --git a/package/libv4l/libv4l.mk b/package/libv4l/libv4l.mk
index b11c8975d1..4dc0f15f94 100644
--- a/[package/libv4l/libv4l.mk](https://git.busybox.net/buildroot/tree/package/libv4l/libv4l.mk?id=1fd67fcfc816d43352d911642f91c51be0c64547)
+++ b/[package/libv4l/libv4l.mk](https://git.busybox.net/buildroot/tree/package/libv4l/libv4l.mk?id=7b2da3caaf87e44b0e3a8d72d43135b123e38bb6)
@@ -71,8 +71,8 @@ LIBV4L_CONF_ENV += \
 	ac_cv_prog_MOC=$(HOST_DIR)/bin/moc \
 	ac_cv_prog_RCC=$(HOST_DIR)/bin/rcc \
 	ac_cv_prog_UIC=$(HOST_DIR)/bin/uic
-# qt5 needs c++11 (since qt-5.7)
-LIBV4L_CONF_ENV += CXXFLAGS="$(TARGET_CXXFLAGS) -std=c++11"
+# qt5 needs c++11 (since qt-5.7)/use gnu++11 for typeof support
+LIBV4L_CONF_ENV += CXXFLAGS="$(TARGET_CXXFLAGS) -std=gnu++11"
 else
 LIBV4L_CONF_OPTS += --disable-qv4l2
 endif

Change libv4l.mk or pull this commit from upstream

https://git.busybox.net/buildroot/commit/package/libv4l/libv4l.mk?id=7b2da3caaf87e44b0e3a8d72d43135b123e38bb6

[shirok1]

The following patches are what I tried at first, indicating which files won't compile without this:

diff --recursive --text --unified --new-file a/utils/common/v4l2-tpg.h b/utils/common/v4l2-tpg.h
--- a/utils/common/v4l2-tpg.h
+++ b/utils/common/v4l2-tpg.h
@@ -30,8 +30,8 @@
 
 #define tpg_min(a,b)	((a) < (b) ? (a) : (b))
 #define tpg_max(a,b)	((a) > (b) ? (a) : (b))
-#define min3(x, y, z) tpg_min((typeof(x))tpg_min(x, y), z)
-#define max3(x, y, z) tpg_max((typeof(x))tpg_max(x, y), z)
+#define min3(x, y, z) tpg_min((__typeof__(x))tpg_min(x, y), z)
+#define max3(x, y, z) tpg_max((__typeof__(x))tpg_max(x, y), z)
 #define array_size(a, b) ((a) * (b))
 #define array3_size(a, b, c) ((a) * (b) * (c))
 
@@ -46,9 +46,9 @@
 }
 
 #define clamp(val, min, max) ({			\
-	typeof(val) __val = (val);		\
-	typeof(min) __min = (min);		\
-	typeof(max) __max = (max);		\
+	__typeof__(val) __val = (val);		\
+	__typeof__(min) __min = (min);		\
+	__typeof__(max) __max = (max);		\
 	(void) (&__val == &__min);		\
 	(void) (&__val == &__max);		\
 	__val = __val < __min ? __min: __val;	\
diff --recursive --text --unified --new-file a/utils/common/v4l2-tpg.patch b/utils/common/v4l2-tpg.patch
--- a/utils/common/v4l2-tpg.patch
+++ b/utils/common/v4l2-tpg.patch
@@ -198,8 +198,8 @@
 +
 +#define tpg_min(a,b)	((a) < (b) ? (a) : (b))
 +#define tpg_max(a,b)	((a) > (b) ? (a) : (b))
-+#define min3(x, y, z) tpg_min((typeof(x))tpg_min(x, y), z)
-+#define max3(x, y, z) tpg_max((typeof(x))tpg_max(x, y), z)
++#define min3(x, y, z) tpg_min((__typeof__(x))tpg_min(x, y), z)
++#define max3(x, y, z) tpg_max((__typeof__(x))tpg_max(x, y), z)
 +#define array_size(a, b) ((a) * (b))
 +#define array3_size(a, b, c) ((a) * (b) * (c))
 +
@@ -214,9 +214,9 @@
 +}
 +
 +#define clamp(val, min, max) ({			\
-+	typeof(val) __val = (val);		\
-+	typeof(min) __min = (min);		\
-+	typeof(max) __max = (max);		\
++	__typeof__(val) __val = (val);		\
++	__typeof__(min) __min = (min);		\
++	__typeof__(max) __max = (max);		\
 +	(void) (&__val == &__min);		\
 +	(void) (&__val == &__max);		\
 +	__val = __val < __min ? __min: __val;	\

This is just a demonstration. DON'T ADD THIS PATCH.