[libc] Fix feature check for riscv (#145169)

This PR fixes the feature detection for RISC-V floating-point support in
LLVM's libc implementation.

The `__riscv_flen` macro represents the floating-point register width in
bits (32, 64, or 128). Since Extension D is specifically documented as
implying F, we can use simple >= comparisons to detect them.

For half-precision support, the implementation checks for the Zfhmin
extension as RVA22 and RVA23 profiles only require Zfhmin rather than
the full Zfh extension. Zfh also implies Zfhmin, so checking for Zfhmin
should cover all cases.

Author: mikhailramalho

libc/src/__support/macros/properties/cpu_features.h

@@ -61,15 +61,15 @@
 
 #if defined(__riscv_flen)
 // https://github.com/riscv-non-isa/riscv-c-api-doc/blob/main/src/c-api.adoc
-#if (__riscv_flen & 0x10)
+#if (__riscv_arch_test && __riscv_zfhmin)
 #define LIBC_TARGET_CPU_HAS_RISCV_FPU_HALF
 #define LIBC_TARGET_CPU_HAS_FPU_HALF
 #endif // LIBC_TARGET_CPU_HAS_RISCV_FPU_HALF
-#if (__riscv_flen & 0x20)
+#if (__riscv_flen >= 32)
 #define LIBC_TARGET_CPU_HAS_RISCV_FPU_FLOAT
 #define LIBC_TARGET_CPU_HAS_FPU_FLOAT
 #endif // LIBC_TARGET_CPU_HAS_RISCV_FPU_FLOAT
-#if (__riscv_flen & 0x40)
+#if (__riscv_flen >= 64)
 #define LIBC_TARGET_CPU_HAS_RISCV_FPU_DOUBLE
 #define LIBC_TARGET_CPU_HAS_FPU_DOUBLE
 #endif // LIBC_TARGET_CPU_HAS_RISCV_FPU_DOUBLE