build(arch): provide OSMesa via mesa-amber extraction (#624)

Closes #623

Arch's modern `mesa` no longer ships classic `libOSMesa`, which
BambuStudio links against (`-lOSMesa`), so the Arch build failed at link
time.

- `linux.d/arch`: extract `libOSMesa.so.8` (+ its `libglapi.so.0`
dependency) from the `mesa-amber` package during the dependency step,
without installing it (mesa-amber conflicts with mesa). This lets the
link succeed while keeping modern mesa.
- `scripts/build_pkg_arch.sh`: bundle both libs into the package so it
also runs on a stock Arch system whose mesa no longer provides them.

Verified: Arch single-distro build #14 on `ci/develop/linux-x86_64` is
green and produced `bambustudio-02.08.00.50-1-x86_64.pkg.tar.zst`.

Author: BenJule

linux.d/arch

@@ -65,6 +65,26 @@ if [[ -n "$UPDATE_LIB" ]]
 then
     sudo pacman -Syu --noconfirm
     sudo pacman -S --noconfirm --needed ${REQUIRED_DEV_PACKAGES[@]}
+
+    # Arch's modern mesa no longer ships classic OSMesa, which BambuStudio links
+    # against (-lOSMesa). mesa-amber still provides it but conflicts with mesa, so
+    # pull libOSMesa (+ its libglapi dependency) out of the mesa-amber package
+    # without installing it.
+    if [ ! -e /usr/lib/libOSMesa.so ]; then
+        sudo pacman -Sw --noconfirm mesa-amber
+        AMBER=$(ls /var/cache/pacman/pkg/mesa-amber-*.pkg.tar.zst 2>/dev/null | head -1)
+        if [ -n "$AMBER" ]; then
+            TMP=$(mktemp -d)
+            sudo bsdtar -xf "$AMBER" -C "$TMP" usr/lib/libOSMesa.so.8.0.0 usr/lib/libglapi.so.0.0.0
+            sudo cp -a "$TMP"/usr/lib/libOSMesa.so.8.0.0 "$TMP"/usr/lib/libglapi.so.0.0.0 /usr/lib/
+            sudo ln -sf libOSMesa.so.8.0.0 /usr/lib/libOSMesa.so.8
+            sudo ln -sf libOSMesa.so.8    /usr/lib/libOSMesa.so
+            sudo ln -sf libglapi.so.0.0.0 /usr/lib/libglapi.so.0
+            sudo ln -sf libglapi.so.0     /usr/lib/libglapi.so
+            rm -rf "$TMP"
+        fi
+    fi
+
     echo -e "done\n"
     exit 0
 fi

scripts/build_pkg_arch.sh

@@ -49,6 +49,20 @@ done
 
 install -m 755 "$APPDIR/bin/bambu-studio" "$STAGING/usr/lib/${PKGNAME}/"
 find "$APPDIR/bin" -name "*.so*" -exec install -m 755 {} "$STAGING/usr/lib/${PKGNAME}/" \;
+
+# Bundle libOSMesa (+ its libglapi dependency). Arch's modern mesa no longer
+# ships classic OSMesa, which BambuStudio links against (-lOSMesa); linux.d/arch
+# extracts them from mesa-amber into /usr/lib during the dependency step, so pull
+# them into the package as well (the launcher sets LD_LIBRARY_PATH to this dir).
+for L in libOSMesa.so.8.0.0 libglapi.so.0.0.0; do
+    [ -e "/usr/lib/$L" ] && install -m 755 "/usr/lib/$L" "$STAGING/usr/lib/${PKGNAME}/"
+done
+(
+    cd "$STAGING/usr/lib/${PKGNAME}"
+    [ -e libOSMesa.so.8.0.0 ] && ln -sf libOSMesa.so.8.0.0 libOSMesa.so.8
+    [ -e libglapi.so.0.0.0 ]  && ln -sf libglapi.so.0.0.0  libglapi.so.0
+    true
+)
 cp -r "$APPDIR/resources" "$STAGING/usr/lib/${PKGNAME}/"
 
 cat > "$STAGING/usr/bin/${PKGNAME}" << 'WRAPPER'