Fix warning about comparison of integer expressions of different signedness

[giordano]

This was done in #50172 only for x86 and the fallback platform:

julia/src/processor_x86.cpp

Line 883 in e618369

if (match.best_idx == (uint32_t)-1)

julia/src/processor_fallback.cpp

Line 182 in e618369

if (match_idx == (uint32_t)-1)

but based on the warning

    CC src/processor.o
In file included from /home/mose/repo/julia/src/processor.cpp:1009:
/home/mose/repo/julia/src/processor_arm.cpp: In function 'uint32_t ARM::sysimg_init_cb(const void*, jl_value_t**)':
/home/mose/repo/julia/src/processor_arm.cpp:1606:24: warning: comparison of integer expressions of different signedness: 'uint32_t' {aka 'unsigned int'} and 'int' [-Wsign-compare]
 1606 |     if (match.best_idx == -1)
      |         ~~~~~~~~~~~~~~~^~~~~

I guess we should do the same also for this architecture.

[gbaraldi]

Should we just use UINTMAX here?