[compiler-rt][AVR] Use correct return value for __ledf2, __lesf2, etc

[aykevl]

Summary

Previously the default was long, which is 32-bit on AVR. But avr-gcc expects a smaller value: it reads the return value from r24.

This is actually a regression from https://reviews.llvm.org/D98205. Before D98205, the return value was an enum (which was 2 bytes in size) which was compatible with the 1-byte return value that avr-gcc was expecting. But long is 4 bytes and thus places the significant return value in a different register.

[compnerd]

Thanks!

compiler-rt/lib/builtins/fp_compare_impl.inc

 // same way as GCC expects (since otherwise GCC-generated __builtin_isinf
 // returns true for finite 128-bit floating-point numbers).
 #ifdef __aarch64__
 // AArch64 GCC overrides libgcc_cmp_return to use int instead of long.
 typedef int CMP_RESULT;
 #elif __SIZEOF_POINTER__ == 8 && __SIZEOF_LONG__ == 4
 // LLP64 ABIs use long long instead of long.
 typedef long long CMP_RESULT;
+#elif __AVR__
+// AVR uses a single byte for the return value.
+typedef char CMP_RESULT;
 #else
 // Otherwise the comparison functions return long.
 typedef long CMP_RESULT;
 #endif
 
 #if !defined(__clang__) && defined(__GNUC__)
 // GCC uses a special __libgcc_cmp_return__ mode to define the return type, so
 // check that we are ABI-compatible when compiling the builtins with GCC.