[libcxx] Make test case fmt specifiers more portable
These printf()s fail to compile like so on hexagon:
.../tools/llvm-top/libcxx/test/std/utilities/charconv/charconv.msvc/test.cpp:94:23: error: format specifies type 'unsigned int' but the argument has type 'unsigned long' [-Werror,-Wformat]
printf("%u ", elem);
~~ ^~~~
%lu
.../tools/llvm-top/libcxx/test/std/utilities/charconv/charconv.msvc/test.cpp:569:56: error: format specifies type 'unsigned int' but the argument has type 'uint32_t' (aka 'unsigned long') [-Werror,-Wformat]
fprintf(stderr, "%s failed for 0x%08X\n", msg, bits);
~~~~ ^~~~
%08lX
.../tools/llvm-top/libcxx/test/std/utilities/charconv/charconv.msvc/test.cpp:1096:43: error: format specifies type 'unsigned int' but the argument has type 'unsigned long' [-Werror,-Wformat]
printf("Randomized test cases: %u\n", PrefixesToTest * Fractions);
~~ ^~~~~~~~~~~~~~~~~~~~~~~~~~
%lu
Differential Revision: https://reviews.llvm.org/D120532