Sync FuchsiaConfig with downstream's custom_scudo_config.h (llvm#89244)

Downstream disabled EnableContiguousRegions on RISCV-64 to avoid
running out of virtual memory, but our tests still use the internal
FuchsiaConfig class, which therefore needs to be changed too.

compiler-rt/lib/scudo/standalone/allocator_config.h

@@ -146,6 +146,7 @@ struct FuchsiaConfig {
     // Support 39-bit VMA for riscv-64
     static const uptr RegionSizeLog = 28U;
     static const uptr GroupSizeLog = 19U;
+    static const bool EnableContiguousRegions = false;
 #else
     static const uptr RegionSizeLog = 30U;
     static const uptr GroupSizeLog = 21U;