clean up rtx constant pool

[David Edelsohn]

	This patch breaks PowerPC AIX and PPC64 Linux bootstrap.

./xgcc -B./ -B/farm/dje/install/powerpc-ibm-aix5.2.0.0-20040130/powerpc-ibm-aix5.2.0.0/bin/ -isystem /farm/dje/install/powerpc-ibm-aix5.2.0.0-20040130/powerpc-ibm-aix5.2.0.0/include -isystem /farm/dje/install/powerpc-ibm-aix5.2.0.0-20040130/powerpc-ibm-aix5.2.0.0/sys-include -L/tmp/powerpc-ibm-aix5.2.0.0-20040130/gcc/../ld -O2  -DIN_GCC    -W -Wall -Wwrite-strings -Wstrict-prototypes -Wmissing-prototypes -Wold-style-definition  -isystem ./include   -g -DHAVE_GTHR_DEFAULT -DIN_LIBGCC2 -D__GCC_FLOAT_NOT_NEEDED  -I. -I -I/farm/dje/src/src/gcc -I/farm/dje/src/src/gcc/ -I/farm/dje/src/src/gcc/../include -I../intl  -DL_floatdidf -c /farm/dje/src/src/gcc/libgcc2.c -o libgcc/./_floatdidf.o
/farm/dje/src/src/gcc/libgcc2.c: In function `__floatdidf':
/farm/dje/src/src/gcc/libgcc2.c:1298: internal compiler error: Illegal instruction

Maybe testing on more than one platform would have been prudent?

David