Rename zero_realloc option "strict" to "alloc".

With realloc(ptr, 0) being UB per C23, the option name "strict" makes less sense
now.  Rename to "alloc" which describes the behavior.

test/unit/zero_realloc_alloc.c

@@ -24,7 +24,7 @@ deallocated() {
 	return deallocated;
 }
 
-TEST_BEGIN(test_realloc_strict) {
+TEST_BEGIN(test_realloc_alloc) {
 	void *ptr = mallocx(1, 0);
 	expect_ptr_not_null(ptr, "Unexpected mallocx error");
 	uint64_t allocated_before = allocated();
@@ -44,5 +44,5 @@ TEST_END
 int
 main(void) {
 	return test(
-	    test_realloc_strict);
+	    test_realloc_alloc);
 }

test/unit/zero_realloc_alloc.sh

@@ -0,0 +1,3 @@
+#!/bin/sh
+
+export MALLOC_CONF="zero_realloc:alloc"

test/unit/zero_realloc_strict.sh

@@ -1,3 +0,0 @@
-#!/bin/sh
-
-export MALLOC_CONF="zero_realloc:strict"