Bug 19054 – alloca() crashes with SEGFAULT after an exception

it seems RCX is corrupt after the exception (which has finished handling and all), which AFAICT should hold the size of the temp stack size ``` import core.stdc.stdlib: alloca; void main() { void* p1 = alloca(10); writeln(p1); try { throw new Exception("foo"); } catch (Exception ex) { writeln(ex.msg); } void* p2 = alloca(10); // <<< SEGFAULT on 0x7ffffffff000 //rax 0x7fffffffd7b0 140737488345008 //rbx 0x3 3 //rcx 0x1ffffffffffffcf8 2305843009213693176 //rdx 0x7fffffffd870 140737488345200 //rsi 0x7ffffffff000 140737488351232 //rdi 0x7fffffffeff0 140737488351216 //rbp 0x7fffffffd900 0x7fffffffd900 //rsp 0x7fffffffd848 0x7fffffffd848 writeln(p2); } ```

DMD64 D Compiler v2.080.0

i mentioned RCX because of https://github.com/dlang/druntime/blob/9a8edfb48e4842180c706ee26ebd8edb10be53f4/src/rt/alloca.d#L230

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