MJIT: Change default --mjit-max-cache back to 100

These days we benchmark MJIT using yjit-bench. The warmup duration in
yjit-bench is very short, so compiling many methods comes at a cost even
while it's actually optimal for MJIT to compile everything / tens of
thousands of methods once it reaches the peak performance.

yjit-bench doesn't necessarily represent the peak performance on production.
It measures the performance of Ruby 30~60s after boot. If your JIT takes
more than 1 minute to warm up, there's no way for the JIT to make the numbers
good on yjit-bench.

Until we make MJIT's compilation much faster, we don't afford compiling
10,000 methods on yjit-bench.

This change alone makes MJIT's benchmark number on railsbench 2x better :p

NEWS.md

@@ -445,6 +445,7 @@ The following deprecated APIs are removed.
   * As a result, Microsoft Visual Studio (MSWIN) is no longer supported.
 * MinGW is no longer supported. [[Feature #18824]]
 * Rename `--mjit-min-calls` to `--mjit-call-threshold`.
+* Change default `--mjit-max-cache` back from 10000 to 100.
 
 ## Static analysis
 

mjit.c

@@ -1626,7 +1626,7 @@ system_tmpdir(void)
 // Minimum value for JIT cache size.
 #define MIN_CACHE_SIZE 10
 // Default permitted number of units with a JIT code kept in memory.
-#define DEFAULT_MAX_CACHE_SIZE 10000
+#define DEFAULT_MAX_CACHE_SIZE 100
 // A default threshold used to add iseq to JIT.
 #define DEFAULT_CALL_THRESHOLD 10000