Add utility to work around bindgen bug 753

rust-lang/rust-bindgen#753

As a result all V4L2_FWHT_FL_* macros have no bindings generated for them.
The github issue describes a suggested workaround, which is applied in
this patch which adds a dedicated "runbindgen" utility, and is centered
around using a wrapper C header file for the problematic header and
defining a custom parse callback.

This works for _BITUL(), but unfortunately not for GENMASK() found in
v4l2-controls.h, which is included from videodev2.h. However, there are
just 2 invocations of GENMASK, so in the fix753.h wrapper we can #undef
the 2 masks and define them manually.

To generate bindings - inside runbindgen directory:

cargo run -- -o ../videodev2_64.rs  -I /path/to/kerneldir/usr/include/
cargo run -- -o ../videodev2_32.rs  -I /path/to/kerneldir/usr/include/ -s /usr/i686-linux-gnu/ -t i686-linux-gnu

Cargo.toml

@@ -2,4 +2,5 @@
 members = [
     "lib",
     "ffi",
+    "lib/src/bindings/runbindgen",
 ]

lib/Cargo.toml

@@ -26,4 +26,11 @@ utils = { path = "../utils" }
 # For convenience we are building the bindings manually and integrating them with
 # the crate. They are generated as follows:
 # bindgen /usr/include/linux/videodev2.h --output src/bindings/videodev2_64.rs
-# bindgen /usr/include/linux/videodev2.h --output src/bindings/videodev2_32.rs -- --target=i686-unknown-linux-gnu
+# bindgen /usr/include/linux/videodev2.h --output src/bindings/videodev2_32.rs -- --target=i686-unknown-linux-gnu
+#
+# In case we want to use locally installed headers (make headers_install in kernel source directory) we need to pass clang args:
+# bindgen usr/include/linux/videodev2.h --output videodev2_64.rs -- -Iusr/include
+# otherwise clang will mix up system-wide headers with locally installed ones resulting in inconsistent output.
+#
+# For 32-bit headers you might need to install libc6-dev-i386-cross or a similar package, and then
+# bindgen usr/include/linux/videodev2.h --output videodev2_32.rs -- --sysroot=/usr/i686-linux-gnu/ --target=i686-linux-gnu -Iusr/include

lib/src/bindings/runbindgen/Cargo.toml

@@ -0,0 +1,10 @@
+[package]
+name = "runbindgen"
+version = "0.1.0"
+edition = "2021"
+
+# See more keys and their definitions at https://doc.rust-lang.org/cargo/reference/manifest.html
+
+[dependencies]
+bindgen = "0.63.0"
+clap = { version = "4.0", features = ["derive"]}

lib/src/bindings/runbindgen/fix753.h

@@ -0,0 +1,17 @@
+#undef V4L2_FWHT_FL_COMPONENTS_NUM_MSK
+#undef V4L2_FWHT_FL_PIXENC_MSK
+
+MARK_FIX_753(V4L2_FWHT_FL_IS_INTERLACED);
+MARK_FIX_753(V4L2_FWHT_FL_IS_BOTTOM_FIRST);
+MARK_FIX_753(V4L2_FWHT_FL_IS_ALTERNATE);
+MARK_FIX_753(V4L2_FWHT_FL_IS_BOTTOM_FIELD);
+MARK_FIX_753(V4L2_FWHT_FL_LUMA_IS_UNCOMPRESSED);
+MARK_FIX_753(V4L2_FWHT_FL_CB_IS_UNCOMPRESSED);
+MARK_FIX_753(V4L2_FWHT_FL_CR_IS_UNCOMPRESSED);
+MARK_FIX_753(V4L2_FWHT_FL_CHROMA_FULL_HEIGHT);
+MARK_FIX_753(V4L2_FWHT_FL_CHROMA_FULL_WIDTH);
+MARK_FIX_753(V4L2_FWHT_FL_ALPHA_IS_UNCOMPRESSED);
+MARK_FIX_753(V4L2_FWHT_FL_I_FRAME);
+
+#define V4L2_FWHT_FL_COMPONENTS_NUM_MSK (7 << V4L2_FWHT_FL_COMPONENTS_NUM_OFFSET)
+#define V4L2_FWHT_FL_PIXENC_MSK (3 << V4L2_FWHT_FL_PIXENC_OFFSET)