PR27829: Support floating point values passed through sdt.h markers

PR27829: Support floating point values passed through sdt.h markers

Add the type to the individual arg entries in the .notes.stapsdt section;
currently SP@A, where S is optional '-' sign, P is precision of type and A is
address.  Revised format is SPT@A where T is optional 'f' for float variables.
Add x8664 float registers xmm8 - xmm15 and aarch64 float registers v8 - v31.
Parse the type field; result is currently ignored.  asm statements are
restricted to 30 arguments; sdt probes can have up to 12 arguments.  To fit
this into a single asm statement, precision and type are encoded into a single
field: 0xSSTT where SS is the precision and TT is the type as encoded by
__builtin_classify_type.  The sign S, precision P, and type T are decoded by
_SDT_SIGN, _SDT_SIZE, and _SDT_TYPE.  Test that the revised
.notes.stapsdt section interacts correctly with eu-elfutils and gdb.