[libc][obvious] Add back the accidentally removed MPFRNumber destructor.

GitOrigin-RevId: 1948acb61b1d900b43fa457b3517de2d7beacd63
diff --git a/utils/MPFRWrapper/MPFRUtils.cpp b/utils/MPFRWrapper/MPFRUtils.cpp
index 86882d0..1ee5cb1 100644
--- a/utils/MPFRWrapper/MPFRUtils.cpp
+++ b/utils/MPFRWrapper/MPFRUtils.cpp
@@ -70,6 +70,10 @@
     mpfr_set(value, other.value, MPFR_RNDN);
   }
 
+  ~MPFRNumber() {
+    mpfr_clear(value);
+  }
+
   MPFRNumber &operator=(const MPFRNumber &rhs) {
     mpfr_set(value, rhs.value, MPFR_RNDN);
     return *this;