Fix #8349: Add const to Max Array C/C++ examples where applicable. (#8350)

As noted by Matt during his [Advent of Compiler Optimizations - Episode
20: Vectorization
[0:55]](https://www.youtube.com/watch?v=d68x8TF7XJs&t=55s), `const` can
and should be introduced here.

We don't need the elements of `y` to be modifiable.

Closes #8349 

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examples/c++/Max_array.cpp

@@ -1,4 +1,4 @@
-void maxArray(double* x, double* y) {
+void maxArray(double* x, const double* y) {
     for (int i = 0; i < 65536; i++) {
         if (y[i] > x[i]) x[i] = y[i];
     }

examples/c++/Max_array_(Optimized).cpp

@@ -1,7 +1,7 @@
 // Compile with -O3 -march=native to see autovectorization
 typedef double *__attribute__((aligned(64))) aligned_double;
 
-void maxArray(aligned_double __restrict x, aligned_double __restrict y) {
+void maxArray(aligned_double __restrict x, const aligned_double __restrict y) {
     for (int i = 0; i < 65536; i++) {
         x[i] = ((y[i] > x[i]) ? y[i] : x[i]);
     }

examples/c/Max_array.c

@@ -1,4 +1,4 @@
-void maxArray(double* x, double* y) {
+void maxArray(double* x, const double* y) {
     int i;
 
     for (i = 0; i < 65536; i++) {