[sanitizer_common] Fix signal_line.cpp on SPARC (llvm#100535)

```
  SanitizerCommon-ubsan-sparc-Linux :: Linux/signal_line.cpp
```
currently `FAIL`s on Linux/sparc64 (32 and 64-bit) for `n == 2`. Instead
of the expected `SIGSEGV`, the test dies with `SIGBUS`. `strace` reveals
that this is due to a unaligned access:
```
--- SIGBUS {si_signo=SIGBUS, si_code=BUS_ADRALN, si_addr=0x1} ---
```
which is to be expected on a strict-alignment target like SPARC. Fixed
by changing the invalid pointer to be better aligned.

Tested on `sparc64-unknown-linux-gnu` and `x86_64-pc-linux-gnu`.

compiler-rt/test/sanitizer_common/TestCases/Linux/signal_line.cpp

@@ -20,7 +20,8 @@ int main(int argc, char **argv) {
   // CHECK1: SUMMARY: [[SAN]]: SEGV {{.*}}signal_line.cpp:[[@LINE-2]]:[[TAB]] in main
 
   if (n == 2)
-    *((volatile int *)0x1) = __LINE__;
+    // Allow for strict-alignment targets that require natural alignment.
+    *((volatile int *)0x8) = __LINE__;
   // CHECK2: #{{[0-9]+ .*}}main {{.*}}signal_line.cpp:[[@LINE-1]]:[[TAB:[0-9]+]]
   // CHECK2: SUMMARY: [[SAN]]: SEGV {{.*}}signal_line.cpp:[[@LINE-2]]:[[TAB]] in main
 }