gitian: use a wrapped gcc/g++ to avoid the need for a system change

C_INCLUDE_PATH and CPLUS_INCLUDE_PATH work globally as though -isystem was used
for each invocation.

Since that changes the build results, force a rebuild of x86 depends by adding
the value to $HOST_ID_SALT.

contrib/gitian-descriptors/gitian-linux.yml

@@ -33,12 +33,6 @@ remotes:
 files: []
 script: |
 
-  #unlock sudo
-  echo "ubuntu" | sudo -S true
-
-  sudo mkdir -p /usr/include/i386-linux-gnu/
-  sudo ln -s /usr/include/x86_64-linux-gnu/asm /usr/include/i386-linux-gnu/asm
-
   WRAP_DIR=$HOME/wrapped
   HOSTS="i686-pc-linux-gnu x86_64-linux-gnu arm-linux-gnueabihf aarch64-linux-gnu"
   CONFIGFLAGS="--enable-glibc-back-compat --enable-reduce-exports --disable-bench --disable-gui-tests"
@@ -90,11 +84,45 @@ script: |
   create_per-host_faketime_wrappers "2000-01-01 12:00:00"
   export PATH=${WRAP_DIR}:${PATH}
 
+  EXTRA_INCLUDES_BASE=$WRAP_DIR/extra_includes
+  mkdir -p $EXTRA_INCLUDES_BASE
+
+  # x86 needs /usr/include/i386-linux-gnu/asm pointed to /usr/include/x86_64-linux-gnu/asm,
+  # but we can't write there. Instead, create a link here and force it to be included in the
+  # search paths by wrapping gcc/g++.
+
+  mkdir -p $EXTRA_INCLUDES_BASE/i686-pc-linux-gnu
+  rm -f $WRAP_DIR/extra_includes/i686-pc-linux-gnu/asm
+  ln -s /usr/include/x86_64-linux-gnu/asm $EXTRA_INCLUDES_BASE/i686-pc-linux-gnu/asm
+
+  for prog in gcc g++; do
+  rm -f ${WRAP_DIR}/${prog}
+  cat << EOF > ${WRAP_DIR}/${prog}
+  #!/bin/bash
+  REAL="`which -a ${prog} | grep -v ${WRAP_DIR}/${prog} | head -1`"
+  for var in "\$@"
+  do
+    if [ "\$var" = "-m32" ]; then
+      export C_INCLUDE_PATH="$EXTRA_INCLUDES_BASE/i686-pc-linux-gnu"
+      export CPLUS_INCLUDE_PATH="$EXTRA_INCLUDES_BASE/i686-pc-linux-gnu"
+      break
+    fi
+  done
+  \$REAL \$@
+  EOF
+  chmod +x ${WRAP_DIR}/${prog}
+  done
+
   cd bitcoin
   BASEPREFIX=`pwd`/depends
   # Build dependencies for each host
   for i in $HOSTS; do
+    EXTRA_INCLUDES="$EXTRA_INCLUDES_BASE/$i"
+    if [ -d "$EXTRA_INCLUDES" ]; then
+      export HOST_ID_SALT="$EXTRA_INCLUDES"
+    fi
     make ${MAKEOPTS} -C ${BASEPREFIX} HOST="${i}"
+    unset HOST_ID_SALT
   done
 
   # Faketime for binaries