[libc] Correctly Run Multiple Benchmarks in the Same File (#98467)

There was previously an issue where registering multiple benchmarks in
the same file would only give the results for the last benchmark to run.
This PR fixes the issue.

@jhuber6

Author: jameshu15869

libc/benchmarks/gpu/LibcGpuBenchmark.cpp

@@ -52,11 +52,10 @@ void Benchmark::run_benchmarks() {
   uint64_t id = gpu::get_thread_id();
   gpu::sync_threads();
 
-  for (Benchmark *b : benchmarks)
+  for (Benchmark *b : benchmarks) {
     results[id] = b->run();
-  gpu::sync_threads();
-  if (id == 0) {
-    for (Benchmark const *b : benchmarks) {
+    gpu::sync_threads();
+    if (id == 0) {
       BenchmarkResult all_results = reduce_results(results);
       constexpr auto GREEN = "\033[32m";
       constexpr auto RESET = "\033[0m";

libc/benchmarks/gpu/src/ctype/isalnum_benchmark.cpp

@@ -6,4 +6,16 @@ uint64_t BM_IsAlnum() {
   char x = 'c';
   return LIBC_NAMESPACE::latency(LIBC_NAMESPACE::isalnum, x);
 }
-BENCHMARK(LlvmLibcIsAlNumGpuBenchmark, IsAlnumWrapper, BM_IsAlnum);
+BENCHMARK(LlvmLibcIsAlNumGpuBenchmark, IsAlnum, BM_IsAlnum);
+
+uint64_t BM_IsAlnumCapital() {
+  char x = 'A';
+  return LIBC_NAMESPACE::latency(LIBC_NAMESPACE::isalnum, x);
+}
+BENCHMARK(LlvmLibcIsAlNumGpuBenchmark, IsAlnumCapital, BM_IsAlnumCapital);
+
+uint64_t BM_IsAlnumNotAlnum() {
+  char x = '{';
+  return LIBC_NAMESPACE::latency(LIBC_NAMESPACE::isalnum, x);
+}
+BENCHMARK(LlvmLibcIsAlNumGpuBenchmark, IsAlnumNotAlnum, BM_IsAlnumNotAlnum);