BSS is immutable so mark it as mutable so that mprotect RWX works

see: mimmutable(1)
https://github.com/google/syzkaller/commit/bc009f82ea71c399f19eef28f115ff5cda7be4ba

Index: src/arm_jit.cpp
--- src/arm_jit.cpp.orig
+++ src/arm_jit.cpp
@@ -198,7 +198,8 @@ static u8 recompile_counts[(1<<26)/16];
 // Reduces memory needed for function pointers.
 // FIXME win64 needs this too, x86_32 doesn't
 
-DS_ALIGN(4096) static u8 scratchpad[1<<25];
+DS_ALIGN(4096) static u8 scratchpad[1<<25]
+	__attribute__((section(".openbsd.mutable")));
 static u8 *scratchptr;
 
 struct ASMJIT_API StaticCodeGenerator : public Context