CI Linux: download rav1e build instead of building own

Building rav1e requires nasm 2.15 (if asm is not disabled) while U20
has just 2.14.02, so that the build in CI currently fails, anyways.

Pick sse4 for now but expect using avx2 version later, depending on
UG_ARCH value.

\+ populate PKG_CONFIG_PATH immediately

.github/scripts/Linux/install_others.sh

@@ -78,6 +78,21 @@ install_pipewire() {(
         fi
 )}
 
+install_rav1e() {(
+        # TODO: use avx2 later
+        if expr "${UG_ARCH-}" : '.*avx' >/dev/null; then
+                avx2=avx2
+        fi
+        fpattern="librav1e.*linux-${avx2-sse4}.tar.gz"
+        "${GITHUB_WORKSPACE-.}"/.github/scripts/download-gh-asset.sh xiph/rav1e \
+                "$fpattern" librav1e.tar.gz
+        sudo tar xaf librav1e.tar.gz -C /usr/local
+        sudo rm -rf /usr/local/lib/librav1e.so*
+        sudo sed -i -e 's-prefix=dist-prefix=/usr/local-' \
+                -e 's/-lrav1e/-lrav1e -lm -pthread/' \
+                /usr/local/lib/pkgconfig/rav1e.pc
+)}
+
 # FFmpeg master needs at least v1.3.238 as for 23th Aug '23
 install_vulkan() {(
         # TOREMOVE: FFmpeg doesn't currently build with main (2024-02-09)
@@ -101,7 +116,7 @@ if [ $# -eq 1 ] && { [ "$1" = -h ] || [ "$1" = --help ] || [ "$1" = help ]; }; t
 fi
 
 if [ $# -eq 0 ] || [ $show_help ]; then
-        set -- aja gpujpeg live555 ndi pipewire vulkan ximea
+        set -- aja gpujpeg live555 ndi pipewire rav1e vulkan ximea
 fi
 
 if [ $show_help ]; then

.github/scripts/Linux/prepare.sh

@@ -1,9 +1,10 @@
 #!/bin/bash -eux
 
+export PKG_CONFIG_PATH=/usr/local/qt/lib/pkgconfig:/usr/local/lib/pkgconfig
 printf "%b" "AJA_DIRECTORY=/var/tmp/ntv2\n\
 CPATH=/usr/local/qt/include\n\
 LIBRARY_PATH=/usr/local/qt/lib\n\
-PKG_CONFIG_PATH=/usr/local/qt/lib/pkgconfig\n" >> "$GITHUB_ENV"
+PKG_CONFIG_PATH=$PKG_CONFIG_PATH\n" >> "$GITHUB_ENV"
 printf "/usr/local/qt/bin\n" >> "$GITHUB_PATH"
 
 git config --global user.name "UltraGrid Builder"

.github/scripts/Linux/rav1e.sh

@@ -1,11 +0,0 @@
-#!/bin/sh -eux
-#
-# Builds rav1e but doesn't install it
-
-rustup update
-cargo install cargo-c
-git clone --depth 1 https://github.com/xiph/rav1e.git
-cd rav1e
-cargo build --release
-cargo cinstall --release --destdir=install
-