[Support] - Check nullptr after allocation with malloc in MallocAllocator

[kkretzsch]

Summary

As a follow up of our nullptr check patches,

https://reviews.llvm.org/D34753
https://reviews.llvm.org/D35414

this patch introduces a nullptr checks on the llvm MallocAllocator class itself.

[MatzeB]

LGTM.

include/llvm/Support/Allocator.h

99–101

Don't use braces around 1-line ifs.

include/llvm/Support/Allocator.h

 #include "llvm/ADT/SmallVector.h"
 #include "llvm/Support/Compiler.h"
 #include "llvm/Support/MathExtras.h"
+#include "llvm/Support/ErrorHandling.h"
 #include <algorithm>
 #include <cassert>
 #include <cstddef>

 
   LLVM_ATTRIBUTE_RETURNS_NONNULL void *Allocate(size_t Size,
                                                 size_t /*Alignment*/) {
-    return malloc(Size);
+    void* memPtr =  malloc(Size);
+    if (memPtr == nullptr) {
+      report_bad_alloc_error("Allocation in MallocAllocator failed.");
+    }
+    return memPtr;
   }
 
   // Pull in base class overloads.