This fixes a build issue where `compiler-rt` tried to declare its own
version of the `FE_*` macros, and included `float.h` in order to get the
constants. `compiler-rt` tried to declare these as an enum, and failed
with a syntax error when the constant's literal values were substituted.
SPDX License Identifiers are a more compact / standardized
way of representing file license information.
See: https://spdx.dev/resources/use/#identifiers
This was done with the `ambr` search and replace tool.
ambr --no-parent-ignore --key-from-file --rep-from-file key.txt rep.txt *
