[llvm] [libc] [libc] Move printf long double to simple calc (PR #75414)

[Guillaume Chatelet via llvm-commits]

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@@ -87,14 +87,25 @@ are not recommended to be adjusted except by persons familiar with the Printf
 Ryu Algorithm. Additionally they have no effect when float conversions are
 disabled.
 
+LIBC_COPT_FLOAT_TO_STR_NO_SPECIALIZE_LD
+---------------------------------------
+This flag disables the separate long double conversion implementation. It is
+not based on the Ryu algorithm, instead generating the digits by
+multiplying/dividing the written-out number by 10^9 to get blocks. It's
+significantly faster than INT_CALC, only about 10x slower than MEGA_TABLE,
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gchatelet wrote:

Is this 10% or 10 times? 10x seems like a lot.

https://github.com/llvm/llvm-project/pull/75414