math: extend non-glibc guard to Clang and add exp10 guard

The previous fix (#1398) guarded __builtin_roundeven only for GCC 10+,
assuming Clang always lowers it to an inline llvm.roundeven.* intrinsic.
That assumption is wrong: Clang emits a roundeven()/roundevenf() libm
call on targets without a native rounding instruction (x86 without
SSE4.1, powerpc, sparc, i386, etc.).  On non-glibc systems (musl,
OpenBSD, FreeBSD, MinGW) the symbol is absent, causing:

  undefined reference to 'roundevenf'

Fix: drop the GCC-only restriction and apply the glibc >= 2.25 guard to
all compilers.  Non-glibc platforms fall through to the existing portable
inline fallback.

Also guard __builtin_exp10 / __builtin_exp10f: exp10() is a GNU
extension present only in glibc, so the builtin produces the same class
of link error on musl and other non-glibc libcs.  The fallback
simde_math_pow(10.0, v) / simde_math_powf(10.0f, v) is already present
and correct.

Reported by brad0 in issue #1396.

Author: kjg0724

simde/simde-math.h

@@ -973,13 +973,18 @@ simde_math_fpclass(double v, const int imm8) {
   #endif
 #endif
 
-#if HEDLEY_HAS_BUILTIN(__builtin_exp10) ||  HEDLEY_GCC_VERSION_CHECK(3,4,0)
+/* __builtin_exp10 lowers to exp10() which is a GNU extension available
+ * only in glibc.  Other libcs (musl, OpenBSD, FreeBSD, MinGW, etc.)
+ * lack the symbol and produce a link error.  Fall back to pow(10, v). */
+#if (HEDLEY_HAS_BUILTIN(__builtin_exp10) || HEDLEY_GCC_VERSION_CHECK(3,4,0)) && \
+    defined(__GLIBC__)
   #  define simde_math_exp10(v) __builtin_exp10(v)
 #else
 #  define simde_math_exp10(v) simde_math_pow(10.0, (v))
 #endif
 
-#if HEDLEY_HAS_BUILTIN(__builtin_exp10f) ||  HEDLEY_GCC_VERSION_CHECK(3,4,0)
+#if (HEDLEY_HAS_BUILTIN(__builtin_exp10f) || HEDLEY_GCC_VERSION_CHECK(3,4,0)) && \
+    defined(__GLIBC__)
   #  define simde_math_exp10f(v) __builtin_exp10f(v)
 #else
 #  define simde_math_exp10f(v) simde_math_powf(10.0f, (v))
@@ -1266,17 +1271,16 @@ simde_math_fpclass(double v, const int imm8) {
 #endif
 
 #if !defined(simde_math_roundeven)
-  /* GCC 10+ lowers __builtin_roundeven to a libm roundeven() call when
-   * the target has no native instruction.  roundeven() is C23 and only
-   * available in glibc >= 2.25; other platforms (musl, OpenBSD, MinGW,
-   * etc.) lack the symbol and produce a link error.  Clang lowers the
-   * builtin to an llvm.roundeven.* intrinsic which is always emitted
-   * inline (no libm dependency), so the GCC guard is not needed there. */
+  /* __builtin_roundeven lowers to a roundeven() libm call on targets
+   * without a native rounding instruction (x86 without SSE4.1,
+   * powerpc, sparc, i386, etc.).  roundeven() is C23 and only
+   * available in glibc >= 2.25; other libcs (musl, OpenBSD, FreeBSD,
+   * MinGW, etc.) lack the symbol and produce a link error.  Guard for
+   * all compilers: non-glibc platforms use the inline fallback below. */
   #if \
      ((!defined(HEDLEY_EMSCRIPTEN_VERSION) || HEDLEY_EMSCRIPTEN_VERSION_CHECK(3, 1, 43)) && \
        HEDLEY_HAS_BUILTIN(__builtin_roundeven) && \
-       (!HEDLEY_GCC_VERSION_CHECK(10,0,0) || \
-        (defined(__GLIBC__) && ((__GLIBC__ > 2) || (__GLIBC__ == 2 && __GLIBC_MINOR__ >= 25)))))
+       (defined(__GLIBC__) && ((__GLIBC__ > 2) || (__GLIBC__ == 2 && __GLIBC_MINOR__ >= 25))))
     #define simde_math_roundeven(v) __builtin_roundeven(v)
   #elif defined(simde_math_round) && defined(simde_math_fabs)
     static HEDLEY_INLINE
@@ -1295,13 +1299,12 @@ simde_math_fpclass(double v, const int imm8) {
 
 #if !defined(simde_math_roundevenf)
   /* Same rationale as simde_math_roundeven above; applies to the float
-   * variant.  GCC 10+ requires glibc >= 2.25 for roundevenf(); Clang
-   * is always safe via llvm.roundeven.f32 inline expansion. */
+   * variant.  Both GCC and Clang emit a roundevenf() libm call on
+   * targets without a native instruction. */
   #if \
      ((!defined(HEDLEY_EMSCRIPTEN_VERSION) || HEDLEY_EMSCRIPTEN_VERSION_CHECK(3, 1, 43)) && \
        HEDLEY_HAS_BUILTIN(__builtin_roundevenf) && \
-       (!HEDLEY_GCC_VERSION_CHECK(10,0,0) || \
-        (defined(__GLIBC__) && ((__GLIBC__ > 2) || (__GLIBC__ == 2 && __GLIBC_MINOR__ >= 25)))))
+       (defined(__GLIBC__) && ((__GLIBC__ > 2) || (__GLIBC__ == 2 && __GLIBC_MINOR__ >= 25))))
     #define simde_math_roundevenf(v) __builtin_roundevenf(v)
   #elif defined(simde_math_roundf) && defined(simde_math_fabsf)
     static HEDLEY_INLINE