Unbreak *tf builtins for hexfloat (#82208)

This re-lands cc0065a7

 in a way that 
keeps existing targets working.

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Original commit message:
#68132 ended up removing
__multc3 & __divtc3 from compiler-rt library builds that have
QUAD_PRECISION but not TF_MODE due to missing int128 support. 
I added support for QUAD_PRECISION to use the native hex float long double representation.

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Co-authored-by: Sean Perry <perry@ca.ibm.com>