[clang] [llvm] [AsmWriter] Print `nan`, `pinf`, and `ninf` when applicable (PR #105618)

[Matt Arsenault via cfe-commits]

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@@ -4387,12 +4387,12 @@ Simple Constants
     zeros. So '``s0x0001``' of type '``i16``' will be -1, not 1.
 **Floating-point constants**
     Floating-point constants use standard decimal notation (e.g.
-    123.421), exponential notation (e.g. 1.23421e+2), or a more precise
-    hexadecimal notation (see below). The assembler requires the exact
-    decimal value of a floating-point constant. For example, the
-    assembler accepts 1.25 but rejects 1.3 because 1.3 is a repeating
-    decimal in binary. Floating-point constants must have a
-    :ref:`floating-point <t_floating>` type.
+    123.421), exponential notation (e.g. 1.23421e+2), identifiers for special
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arsenm wrote:

can we just move all FP constants to use C99 hex float format? 

https://github.com/llvm/llvm-project/pull/105618