file(STRINGS): Use isprint() to test character type

Use the more portable `isprint()` function to test characters rather
than using hard-coded hex values.  The function is documented by the C++
standard to return non-zero for the exact range of hex values we
previously hard-coded, so this should not change behavior.

Source/cmFileCommand.cxx

@@ -10,6 +10,7 @@
 
 #include <algorithm>
 #include <assert.h>
+#include <ctype.h>
 #include <memory> // IWYU pragma: keep
 #include <sstream>
 #include <stdio.h>
@@ -609,8 +610,8 @@ bool cmFileCommand::HandleStringsCommand(std::vector<std::string> const& args)
       continue;
     }
 
-    if ((c >= 0x20 && c < 0x7F) || c == '\t' ||
-        (c == '\n' && newline_consume)) {
+    if (c >= 0 && c <= 0xFF &&
+        (isprint(c) || c == '\t' || (c == '\n' && newline_consume))) {
       // This is an ASCII character that may be part of a string.
       // Cast added to avoid compiler warning. Cast is ok because
       // c is guaranteed to fit in char by the above if...