hermetic build: hermetic host tools

Use the glibc prebuilt sysroot as sysroot for all host tools. In order
to use that, also add the prebuilt kernel tools (include, lib64) to
satisfy dependencies like openssl (via boringssl).

Bug: 135570712
Signed-off-by: Matthias Maennich <[email protected]>
Change-Id: I20bc005488b166b8363c17af9a602c66f7db6298

_setup_env.sh

@@ -108,6 +108,18 @@ if [ -n "${HERMETIC_TOOLCHAIN}" ]; then
   # (e.g. debug info)
   export KCPPFLAGS="-ffile-prefix-map=${ROOT_DIR}/="
 
+  # set the common sysroot
+  sysroot_flags+="--sysroot=${ROOT_DIR}/build/build-tools/sysroot "
+
+  # add openssl (via boringssl) and other prebuilts into the lookup path
+  cflags+="-I${ROOT_DIR}/prebuilts/kernel-build-tools/linux-x86/include "
+
+  # add openssl and further prebuilt libraries into the lookup path
+  ldflags+="-Wl,-rpath,${ROOT_DIR}/prebuilts/kernel-build-tools/linux-x86/lib64 "
+  ldflags+="-L ${ROOT_DIR}/prebuilts/kernel-build-tools/linux-x86/lib64 "
+
+  export HOSTCFLAGS="$sysroot_flags $cflags"
+  export HOSTLDFLAGS="$sysroot_flags $ldflags"
 fi
 
 for PREBUILT_BIN in "${PREBUILTS_PATHS[@]}"; do

build-tools/sysroot

@@ -0,0 +1 @@
+../../prebuilts/gcc/linux-x86/host/x86_64-linux-glibc2.17-4.8/sysroot

hermetic/Dockerfile

@@ -5,8 +5,6 @@ RUN apt-get -y update                            \
 # Those are likely essential
     git                                          \
 # To be removed
-    libc6-dev                                    \
-    libssl-dev                                   \
     rsync                                        \
 && apt-get clean                                 \
 && rm -rf /var/lib/apt/lists/*