A prefix for default library/include search paths

This patch is useful for cross compilers. Without this patch tcc
tries to use the host's libraries, crt*.o and include files.
The patch prepends a string to all default paths. The string can
be passed to configure with --sysroot=string.

  Daniel

configure

@@ -26,6 +26,7 @@ libdir=""
 tccdir=""
 includedir=""
 mandir=""
+sysroot=""
 cross_prefix=""
 cc="gcc"
 host_cc="gcc"
@@ -102,6 +103,8 @@ for opt do
   ;;
   --mandir=*) mandir=`echo $opt | cut -d '=' -f 2`
   ;;
+  --sysroot=*) sysroot=`echo $opt | cut -d '=' -f 2`
+  ;;
   --source-path=*) source_path=`echo $opt | cut -d '=' -f 2`
   ;;
   --cross-prefix=*) cross_prefix=`echo $opt | cut -d '=' -f 2`
@@ -218,6 +221,7 @@ echo ""
 echo "Advanced options (experts only):"
 echo "  --source-path=PATH       path of source code [$source_path]"
 echo "  --cross-prefix=PREFIX    use PREFIX for compile tools [$cross_prefix]"
+echo "  --sysroot=PREFIX         prepend PREFIX to library/include paths []"
 echo "  --cc=CC                  use C compiler CC [$cc]"
 echo "  --make=MAKE              use specified make [$make]"
 echo ""
@@ -267,6 +271,7 @@ echo "Library directory   $libdir"
 echo "Include directory   $includedir"
 echo "Manual directory    $mandir"
 echo "Doc directory       $docdir"
+echo "Target root prefix  $sysroot"
 echo "Source path      $source_path"
 echo "C compiler       $cc"
 echo "make             $make"
@@ -287,6 +292,7 @@ echo "libdir=$libdir" >> config.mak
 echo "includedir=$includedir" >> config.mak
 echo "mandir=$mandir" >> config.mak
 echo "docdir=$docdir" >> config.mak
+echo "#define CONFIG_SYSROOT \"$sysroot\"" >> $TMPH
 echo "#define CONFIG_TCCDIR \"$tccdir\"" >> $TMPH
 echo "MAKE=$make" >> config.mak
 echo "CC=$cc" >> config.mak