err/err.c: improve err_clear_last_constant_time's portability.

Reviewed-by: NKurt Roeckx <kurt@roeckx.be>
Reviewed-by: NRichard Levitte <levitte@openssl.org>
(Merged from https://github.com/openssl/openssl/pull/7850)

(cherry picked from commit 91d0fd1c2753f0f7d6e0953eed3cfb6eb96d8ff4)

crypto/err/err.c

@@ -880,6 +880,25 @@ int ERR_clear_last_mark(void)
     return 1;
 }
 
+#ifdef UINTPTR_T
+# undef UINTPTR_T
+#endif
+/*
+ * uintptr_t is the answer, but unfortunately C89, current "least common
+ * denominator" doesn't define it. Most legacy platforms typedef it anyway,
+ * so that attempt to fill the gaps means that one would have to identify
+ * that track these gaps, which would be undesirable. Macro it is...
+ */
+#if defined(__VMS) && __INITIAL_POINTER_SIZE==64
+/*
+ * But we can't use size_t on VMS, because it adheres to sizeof(size_t)==4
+ * even in 64-bit builds, which means that it won't work as mask.
+ */
+# define UINTPTR_T unsigned long long
+#else
+# define UINTPTR_T size_t
+#endif
+
 void err_clear_last_constant_time(int clear)
 {
     ERR_STATE *es;
@@ -893,8 +912,8 @@ void err_clear_last_constant_time(int clear)
 
     es->err_flags[top] &= ~(0 - clear);
     es->err_buffer[top] &= ~(0UL - clear);
-    es->err_file[top] = (const char *)((uintptr_t)es->err_file[top] &
-                                       ~((uintptr_t)0 - clear));
+    es->err_file[top] = (const char *)((UINTPTR_T)es->err_file[top] &
+                                       ~((UINTPTR_T)0 - clear));
     es->err_line[top] |= 0 - clear;
 
     es->top = (top + ERR_NUM_ERRORS - clear) % ERR_NUM_ERRORS;