tree-wide: Replace exp10() with our own impl

exp10() has a symbol version > 2.34 on latest glibc. To allow 
dropping our baseline required glibc runtime version to <= 2.34, 
let's add our own version to prevent pulling in the newer symbol 
from glibc.

src/basic/math-util.h

@@ -12,3 +12,8 @@
 /* To avoid x == y and triggering compile warning -Wfloat-equal. This returns false if one of the argument is
  * NaN or infinity. One of the argument must be a floating point. */
 #define fp_equal(x, y) iszero_safe((x) - (y))
+
+/* 10^n. Exact for |n| ≤ 22; otherwise multiplies and may accumulate rounding error. Saturates to
+ * 0.0 or +Inf outside binary64's exponent range; large |n| is capped internally so untrusted
+ * inputs can't cause unbounded work. */
+double xexp10i(int n);