Allow to use libgcc instead of libtcc1

This patch adds a switch --with-libgcc to configure.
When passed it prevents libtcc1.a from being built and links to
/lib/libgcc_s.so.1 instead of PREFIX/lib/tcc/libtcc1.a.

It will work on ARM when using libgcc from GCC >= 4.2.0.
Prior versions don't have the __floatun[sd]i[sdx]f functions.

It won't work on i386 because of two missing symbols emitted when
floats are cast to integers, but users can provide those symbols
(global short constants) in their code if needed.

  Daniel

configure

@@ -19,6 +19,7 @@ TMPH="${TMPDIR1}/tcc-conf-${RANDOM}-$$-${RANDOM}.h"
 
 # default parameters
 build_cross="no"
+use_libgcc="no"
 prefix=""
 execprefix=""
 bindir=""
@@ -127,6 +128,8 @@ for opt do
   ;; 
   --enable-cross) build_cross="yes"
   ;;
+  --with-libgcc) use_libgcc="yes"
+  ;;
   esac
 done
 
@@ -224,6 +227,7 @@ 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 "  --with-libgcc            use /lib/libgcc_s.so.1 instead of libtcc1.a"
 echo ""
 #echo "NOTE: The object files are build at the place where configure is launched"
 exit 1
@@ -279,6 +283,7 @@ echo "CPU              $cpu"
 echo "Big Endian       $bigendian"
 echo "gprof enabled    $gprof"
 echo "cross compilers  $build_cross"
+echo "use libgcc       $use_libgcc"
 
 echo "Creating config.mak and config.h"
 
@@ -345,6 +350,10 @@ fi
 if test "$build_cross" = "yes" ; then
   echo "CONFIG_CROSS=yes" >> config.mak
 fi
+if test "$use_libgcc" = "yes" ; then
+  echo "#define CONFIG_USE_LIBGCC" >> $TMPH
+  echo "CONFIG_USE_LIBGCC=yes" >> config.mak
+fi
 version=`head $source_path/VERSION`
 echo "VERSION=$version" >>config.mak
 echo "#define TCC_VERSION \"$version\"" >> $TMPH