[libc] Enable exp10m1f on RISC-V

Previously, the test was failing due to isnan() and isinf() not being
defined. The patch follows other tests in the same dir and call isnan
and isinf from the FBits class.

Author: mikhailramalho

libc/config/linux/riscv/entrypoints.txt

@@ -451,7 +451,7 @@ set(TARGET_LIBM_ENTRYPOINTS
     libc.src.math.exp
     libc.src.math.exp10
     libc.src.math.exp10f
-    # libc.src.math.exp10m1f
+    libc.src.math.exp10m1f
     libc.src.math.exp2
     libc.src.math.exp2f
     libc.src.math.exp2m1f

libc/test/src/math/exp10m1f_test.cpp

@@ -80,7 +80,7 @@ TEST_F(LlvmLibcExp10m1fTest, InFloatRange) {
   constexpr uint32_t STEP = UINT32_MAX / COUNT;
   for (uint32_t i = 0, v = 0; i <= COUNT; ++i, v += STEP) {
     float x = FPBits(v).get_val();
-    if (isnan(x) || isinf(x))
+    if (FPBits(v).is_nan() || FPBits(v).is_inf())
       continue;
     LIBC_NAMESPACE::libc_errno = 0;
     float result = LIBC_NAMESPACE::exp10m1f(x);
@@ -89,7 +89,8 @@ TEST_F(LlvmLibcExp10m1fTest, InFloatRange) {
     // in the single-precision floating point range, then ignore comparing with
     // MPFR result as MPFR can still produce valid results because of its
     // wider precision.
-    if (isnan(result) || isinf(result) || LIBC_NAMESPACE::libc_errno != 0)
+    if (FPBits(result).is_nan() || FPBits(result).is_inf() ||
+        LIBC_NAMESPACE::libc_errno != 0)
       continue;
     ASSERT_MPFR_MATCH_ALL_ROUNDING(mpfr::Operation::Exp10m1, x,
                                    LIBC_NAMESPACE::exp10m1f(x), 0.5);