ext: Update softfloat to 3d full version

* Add all softfloat source files without any change.
* Remove useless file softfloat.mk.in, since gem5 use Scons.
* Add `use_fast_int64` in SConscript to distinguish src of two strategies for data
  larger than 64 bits.
  * The SoftFloat library uses two strategies to handle data larger than 64bit. One is
    spliting data into `fast_int64`, and the other is using pointer. Two strategies
    are distinguished by macro `SOFTFLOAT_FAST_INT64`. But not all "*.c" files are
    guarded by this macro, which leads to including useless files in compiling progress
    and compiling error. `use_fast_int64` used in SConscript can exclude unnecessary
    files.

Change-Id: I7cec10412c00a35c247299cd92d83cdee9066410
Reviewed-on: https://gem5-review.googlesource.com/c/public/gem5/+/66552
Maintainer: Jason Lowe-Power <power.jg@gmail.com>
Tested-by: kokoro <noreply+kokoro@google.com>
Reviewed-by: Hoa Nguyen <hoanguyen@ucdavis.edu>

ext/softfloat/specialize.h

@@ -39,7 +39,6 @@ SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
 
 #include <stdbool.h>
 #include <stdint.h>
-
 #include "primitiveTypes.h"
 #include "softfloat.h"
 
@@ -56,6 +55,20 @@ extern "C" {
 | The values to return on conversions to 32-bit integer formats that raise an
 | invalid exception.
 *----------------------------------------------------------------------------*/
+#define ui8_fromPosOverflow  0xFF
+#define ui8_fromNegOverflow  0
+#define ui8_fromNaN          0xFF
+#define i8_fromPosOverflow   0x7F
+#define i8_fromNegOverflow   (-0x7F - 1)
+#define i8_fromNaN           0x7F
+
+#define ui16_fromPosOverflow 0xFFFF
+#define ui16_fromNegOverflow 0
+#define ui16_fromNaN         0xFFFF
+#define i16_fromPosOverflow  0x7FFF
+#define i16_fromNegOverflow  (-0x7FFF - 1)
+#define i16_fromNaN          0x7FFF
+
 #define ui32_fromPosOverflow 0xFFFFFFFF
 #define ui32_fromNegOverflow 0
 #define ui32_fromNaN         0xFFFFFFFF