[lldb] Fix some tests failing with gmodules after change to stdlib.h

Commit 82b47b2978 changes the way the stdlib.h
header is structured which seems to cause strange lookup failures in the modules
build. This updates a few failing tests so that they pass with the new
behavior of stdlib.h.

See the discussion in https://reviews.llvm.org/rG82b47b2978405f802a33b00d046e6f18ef6a47be

lldb/test/API/commands/expression/import-std-module/conflicts/main.cpp

@@ -1,5 +1,6 @@
 #include <cstdlib>
 #include <utility>
+#include <cmath>
 
 int main(int argc, char **argv) {
   std::size_t f = argc;

lldb/test/API/commands/expression/static-initializers/main.cpp

@@ -4,7 +4,7 @@ int counter = 0;
 
 void inc_counter() { ++counter; }
 
-void do_abort() { abort(); }
+void do_abort() { std::abort(); }
 
 int main() {
   return 0; // break here

lldb/test/API/lang/cpp/operators/main.cpp

@@ -4,8 +4,8 @@ int side_effect = 0;
 
 struct B { int dummy = 2324; };
 struct C {
-  void *operator new(size_t size) { C* r = ::new C; r->custom_new = true; return r; }
-  void *operator new[](size_t size) { C* r = static_cast<C*>(std::malloc(size)); r->custom_new = true; return r; }
+  void *operator new(std::size_t size) { C* r = ::new C; r->custom_new = true; return r; }
+  void *operator new[](std::size_t size) { C* r = static_cast<C*>(std::malloc(size)); r->custom_new = true; return r; }
   void operator delete(void *p) { std::free(p); side_effect = 1; }
   void operator delete[](void *p) { std::free(p); side_effect = 2; }