llvm-dev is required on Debian

README.md

@@ -75,7 +75,7 @@ sudo apt install git curl autoconf libx11-dev \
     libssl-dev libbz2-dev liblzma-dev libosmesa6-dev libxmu6 libxmu-dev \
     libglu1-mesa-dev libgles2-mesa-dev libegl1-mesa-dev libdbus-1-dev \
     libharfbuzz-dev ccache clang libunwind-dev \
-    libgstreamer1.0-dev libgstreamer-plugins-base1.0-dev libgstreamer-plugins-bad1.0-dev autoconf2.13
+    libgstreamer1.0-dev libgstreamer-plugins-base1.0-dev libgstreamer-plugins-bad1.0-dev autoconf2.13 llvm-dev
 ```
 
 Additionally, you'll need a local copy of GStreamer with a version later than 12.0. You can place it in `support/linux/gstreamer/gst`, or run `./mach bootstrap-gstreamer` to set it up.

python/servo/bootstrap.py

@@ -117,7 +117,7 @@ def linux(context, force=False):
                 'libbz2-dev', 'liblzma-dev',
                 'libosmesa6-dev', 'libxmu6', 'libxmu-dev', 'libglu1-mesa-dev',
                 'libgles2-mesa-dev', 'libegl1-mesa-dev', 'libdbus-1-dev', 'libharfbuzz-dev',
-                'ccache', 'clang', 'autoconf2.13', 'libunwind-dev']
+                'ccache', 'clang', 'autoconf2.13', 'libunwind-dev', 'llvm-dev']
     pkgs_dnf = ['libtool', 'gcc-c++', 'libXi-devel', 'freetype-devel', 'libunwind-devel',
                 'mesa-libGL-devel', 'mesa-libEGL-devel', 'glib2-devel', 'libX11-devel',
                 'libXrandr-devel', 'gperf', 'fontconfig-devel', 'cabextract', 'ttmkfdir',