Add script to download + build libelf and zlib

usage:

```
$ tools/build_deps
$ export RUSTFLAGS="-L $PWD/target/static-libs"
$ cargo b # will now link against libelf and zlib
```

This allows us to have more control on the actual version of
both libraries that libbpf depends on, rather than always using
the ones installed by a package manager or a previous manual
installation.

They are compiled with clang and frame pointers. See comment
for the warnings that were disabled to compile elfutils with clang.

Signed-off-by: Francisco Javier Honduvilla Coto <javierhonduco@gmail.com>

tools/build_deps

@@ -0,0 +1,62 @@
+#!/usr/bin/env bash
+set -o errexit nounset pipefail
+
+NPROC=$(nproc --all)
+ELFUTILS_VERSION="0.188"
+ELFUTILS_SHA_512="585551b2d937d19d1becfc2f28935db1dd1a3d25571a62f322b70ac8da98c1a741a55d070327705df6c3e2ee026652e0b9a3c733b050a0b0ec5f2fc75d5b74b5"
+
+ZLIB_VERSION="1.2.13"
+ZLIB_SHA256="b3a24de97a8fdbc835b9833169501030b8977031bcb54b3b3ac13740f846ab30"
+
+run() {
+    "$@" >/dev/null 2>&1
+}
+
+mkdir -p target/static-libs
+mkdir -p target/static-libs/libz
+mkdir -p target/static-libs/elfutils
+STATIC_LIBS_OUT_PATH="${PWD}/target/static-libs"
+
+run pushd "${STATIC_LIBS_OUT_PATH}"
+
+# Notes:
+# * -fpic is not the same as -FPIC
+# https://gcc.gnu.org/onlinedocs/gcc/Code-Gen-Options.html
+#
+# * cflags required for clang to compile elfutils
+export CFLAGS="-fno-omit-frame-pointer -fpic -Wno-gnu-variable-sized-type-not-at-end -Wno-unused-but-set-parameter"
+export CC=clang
+
+echo "=> Building elfutils"
+run curl -L -O "https://sourceware.org/pub/elfutils/${ELFUTILS_VERSION}/elfutils-${ELFUTILS_VERSION}.tar.bz2"
+if ! sha512sum "elfutils-${ELFUTILS_VERSION}.tar.bz2" | grep -q "$ELFUTILS_SHA_512"; then
+    echo "Checksum for elfutils doesn't match"
+    exit 1
+fi
+
+run tar xjf "elfutils-${ELFUTILS_VERSION}.tar.bz2"
+
+run pushd "elfutils-${ELFUTILS_VERSION}"
+run ./configure --prefix="${STATIC_LIBS_OUT_PATH}/elfutils" --disable-debuginfod --disable-libdebuginfod
+
+run make "-j${NPROC}"
+run make install
+cp "${STATIC_LIBS_OUT_PATH}/elfutils/lib/libelf.a" "${STATIC_LIBS_OUT_PATH}"
+run popd
+
+echo "=> Building zlib"
+run curl -L -O "https://zlib.net/zlib-${ZLIB_VERSION}.tar.gz"
+if ! sha256sum "zlib-${ZLIB_VERSION}.tar.gz" | grep -q "$ZLIB_SHA256"; then
+    echo "Checksum for zlib doesn't match"
+    exit 1
+fi
+run tar xzf zlib-${ZLIB_VERSION}.tar.gz
+
+run pushd "zlib-${ZLIB_VERSION}"
+run ./configure --prefix="${STATIC_LIBS_OUT_PATH}/libz" >/dev/null
+run make "-j${NPROC}" >/dev/null
+run make install >/dev/null
+cp "${STATIC_LIBS_OUT_PATH}/libz/lib/libz.a" "${STATIC_LIBS_OUT_PATH}"
+run popd
+
+run popd

tools/pull_ruby_images

@@ -2,15 +2,15 @@
 
 ruby_versions=(
     2.6.0
-    2.6.3 
-    2.7.1 
+    2.6.3
+    2.7.1
     2.7.4
     2.7.6
-    3.0.0 
-    3.0.4 
-    3.1.2 
+    3.0.0
+    3.0.4
+    3.1.2
 )
 
 for ruby_version in "${ruby_versions[@]}"; do
-    podman pull ruby:$ruby_version
+    podman pull "ruby:$ruby_version"
 done