[dexter-tests] Add attribute optnone to main function

[Carrot]

Summary

The test case optnone-simple-functions.cpp is expected to be compiled unoptimized even under -O2 because of attribute optnone. But this attribute is missed for main function, and caused the fail in https://lab.llvm.org/buildbot/#/builders/217/builds/14046 when it triggered optimizations. This patch fixes that by adding attribute optnone to main function.

[jmorse]

Ah, you're way ahead of me -- this is the correct fix, LGTM!

cross-project-tests/debuginfo-tests/dexter-tests/optnone-simple-functions.cpp

int test5(int test5_val) {
   if (test5_val)  // DexExpectStepOrder(22)
     c = 5;        // DexExpectStepOrder(23)
   return c ? test5_val : test5_val; // DexExpectStepOrder(24)
   // DexLabel('test5_end')
 }
 // DexExpectWatchValue('test5_val', 7, from_line=ref('test5_start'), to_line=ref('test5_end'))
 // DexExpectWatchValue('c', 1, 5, from_line=ref('test5_start'), to_line=ref('test5_end'))
 
+__attribute__((optnone))
 int main() {
   int main_result = 0;
   // DexLabel('main_start')
   main_result = test1(3,4);
   main_result += test2(1,2);
   main_result += test3(5,6);
   main_result += test4(1,9);
   main_result += test5(7);
   return main_result;
   // DexLabel('main_end')
 }
 // DexExpectWatchValue('main_result', 0, 7, 11, 21, 26, 33, from_line=ref('main_start'), to_line=ref('main_end'))