[OpenMP] Remove dependency on LLVM include directory from DeviceRTL (#136359)

Summary:
Currently we depend on a single LLVM include directory. This is actually
only required to define one enum, which is highly unlikely to change.
THis patch makes the `Environment.h` include directory more hermetic so
we no long depend on other libraries. In exchange, we get a simpler
dependency list for the price of hard-coding `1` somewhere. I think it's
a valid trade considering that this flag is highly unlikely to change at
this point.

@ronlieb AMD version
https://gist.github.com/jhuber6/3313e6f957be14dc79fe85e5126d2cb3

offload/DeviceRTL/CMakeLists.txt

@@ -75,10 +75,6 @@ if(${LIBOMPTARGET_GPU_LIBC_SUPPORT})
   list(APPEND clang_opt_flags -DOMPTARGET_HAS_LIBC)
 endif()
 
-# Prepend -I to each list element
-set (LIBOMPTARGET_LLVM_INCLUDE_DIRS_DEVICERTL "${LIBOMPTARGET_LLVM_INCLUDE_DIRS}")
-list(TRANSFORM LIBOMPTARGET_LLVM_INCLUDE_DIRS_DEVICERTL PREPEND "-I")
-
 # Set flags for LLVM Bitcode compilation.
 set(bc_flags -c -flto -std=c++17 -fvisibility=hidden
              ${clang_opt_flags} -nogpulib -nostdlibinc
@@ -88,7 +84,6 @@ set(bc_flags -c -flto -std=c++17 -fvisibility=hidden
              -I${include_directory}
              -I${devicertl_base_directory}/../include
              -I${devicertl_base_directory}/../../libc
-             ${LIBOMPTARGET_LLVM_INCLUDE_DIRS_DEVICERTL}
 )
 
 # first create an object target
@@ -172,7 +167,6 @@ function(compileDeviceRTLLibrary target_name target_triple)
       ${include_directory}
       ${devicertl_base_directory}/../../libc
       ${devicertl_base_directory}/../include
-      ${LIBOMPTARGET_LLVM_INCLUDE_DIRS}
     )
     install(TARGETS ${ide_target_name} EXCLUDE_FROM_ALL)
   endif()

offload/DeviceRTL/src/Kernel.cpp

@@ -21,10 +21,17 @@
 #include "Synchronization.h"
 #include "Workshare.h"
 
-#include "llvm/Frontend/OpenMP/OMPDeviceConstants.h"
-
 using namespace ompx;
 
+// These flags are copied from "llvm/Frontend/OpenMP/OMPDeviceConstants.h" and
+// must be kept in-sync.
+enum OMPTgtExecModeFlags : unsigned char {
+  OMP_TGT_EXEC_MODE_GENERIC = 1 << 0,
+  OMP_TGT_EXEC_MODE_SPMD = 1 << 1,
+  OMP_TGT_EXEC_MODE_GENERIC_SPMD =
+      OMP_TGT_EXEC_MODE_GENERIC | OMP_TGT_EXEC_MODE_SPMD
+};
+
 static void
 inititializeRuntime(bool IsSPMD, KernelEnvironmentTy &KernelEnvironment,
                     KernelLaunchEnvironmentTy &KernelLaunchEnvironment) {
@@ -74,8 +81,7 @@ extern "C" {
 int32_t __kmpc_target_init(KernelEnvironmentTy &KernelEnvironment,
                            KernelLaunchEnvironmentTy &KernelLaunchEnvironment) {
   ConfigurationEnvironmentTy &Configuration = KernelEnvironment.Configuration;
-  bool IsSPMD = Configuration.ExecMode &
-                llvm::omp::OMPTgtExecModeFlags::OMP_TGT_EXEC_MODE_SPMD;
+  bool IsSPMD = Configuration.ExecMode & OMP_TGT_EXEC_MODE_SPMD;
   bool UseGenericStateMachine = Configuration.UseGenericStateMachine;
   if (IsSPMD) {
     inititializeRuntime(/*IsSPMD=*/true, KernelEnvironment,

offload/DeviceRTL/src/Mapping.cpp

@@ -16,8 +16,6 @@
 #include "State.h"
 #include "gpuintrin.h"
 
-#include "llvm/Frontend/OpenMP/OMPGridValues.h"
-
 using namespace ompx;
 
 // FIXME: This resolves the handling for the AMDGPU workgroup size when the ABI

offload/include/Shared/Environment.h

@@ -15,15 +15,7 @@
 
 #include <stdint.h>
 
-#ifdef OMPTARGET_DEVICE_RUNTIME
-#include "DeviceTypes.h"
-#else
-#include "SourceInfo.h"
-
-using IdentTy = ident_t;
-#endif
-
-#include "llvm/Frontend/OpenMP/OMPDeviceConstants.h"
+struct IdentTy;
 
 enum class DeviceDebugKind : uint32_t {
   Assertion = 1U << 0,
@@ -80,7 +72,7 @@ struct DynamicEnvironmentTy {
 struct ConfigurationEnvironmentTy {
   uint8_t UseGenericStateMachine = 2;
   uint8_t MayUseNestedParallelism = 2;
-  llvm::omp::OMPTgtExecModeFlags ExecMode = llvm::omp::OMP_TGT_EXEC_MODE_SPMD;
+  uint8_t ExecMode = 0;
   // Information about (legal) launch configurations.
   //{
   int32_t MinThreads = -1;