Back out too-platform-fussy bits in preempt-test work. I hate this test.

src/rt/rust_internal.h

@@ -67,17 +67,6 @@ struct frame_glue_fns;
 
 static size_t const TIME_SLICE_IN_MS = 10;
 
-// This helps our preemption scheme handle "running on valgrind".
-
-#if defined(__WIN32__)
-#define YIELD_C_THREAD_IF_ON_VALGRIND (void);
-#else
-#define YIELD_C_THREAD_IF_ON_VALGRIND  \
-    if (RUNNING_ON_VALGRIND) {         \
-        pthread_yield();               \
-    }
-#endif
-
 // Every reference counted object should derive from this base class.
 
 template <typename T>

src/rt/rust_timer.cpp

@@ -34,7 +34,6 @@ timer_loop(void *ptr) {
     size_t ms = TIME_SLICE_IN_MS;
 
     while (!timer->exit_flag) {
-        YIELD_C_THREAD_IF_ON_VALGRIND;
 #if defined(__WIN32__)
         Sleep(ms);
 #else

src/rt/rust_upcall.cpp

@@ -1,11 +1,9 @@
 #include "rust_internal.h"
-#include "valgrind.h"
 
 // Upcalls.
 
 #ifdef __GNUC__
 #define LOG_UPCALL_ENTRY(task)                              \
-    YIELD_C_THREAD_IF_ON_VALGRIND;                          \
     (task)->dom->get_log().reset_indent(0);                 \
     (task)->log(rust_log::UPCALL,                           \
                 "> UPCALL %s - task: 0x%" PRIxPTR           \
@@ -15,7 +13,6 @@
     (task)->dom->get_log().indent();
 #else
 #define LOG_UPCALL_ENTRY(task)                              \
-    YIELD_C_THREAD_IF_ON_VALGRIND;                          \
     (task)->dom->get_log().reset_indent(0);                 \
     (task)->log(rust_log::UPCALL,                           \
                 "> UPCALL task: x%" PRIxPTR (task));        \