gromacs: add itt variant (spack#47764)

Permit configuring GROMACS with support for mdrun to trace its timing
regions by calling the ITT API. This permits tools like VTune and
unitrace to augment their analysis with GROMACS-specific annotation.

var/spack/repos/builtin/packages/gromacs/package.py

@@ -296,6 +296,15 @@ class Gromacs(CMakePackage, CudaPackage):
         + "The g++ location is written to icp{c,x}.cfg",
     )
 
+    variant(
+        "itt",
+        default=False,
+        when="@2024:",
+        description="Enable Instrumentation and Tracing Technology (ITT)"
+        + " profiling API (from Intel)",
+    )
+    depends_on("intel-oneapi-vtune", "+itt")
+
     depends_on("fftw-api@3")
     depends_on("[email protected]:3", type="build")
     depends_on("[email protected]:3", type="build", when="@2018:")
@@ -614,6 +623,13 @@ def cmake_args(self):
             options.append("-DGMX_GPU_NB_CLUSTER_SIZE=8")
             options.append("-DGMX_GPU_NB_NUM_CLUSTER_PER_CELL_X=1")
 
+        if "+itt" in self.spec:
+            options.append("-DGMX_USE_ITT=on")
+            options.append(
+                "-DITTNOTIFY_INCLUDE_DIR=%s"
+                % join_path(self.spec["intel-oneapi-vtune"].package.headers)
+            )
+
         if self.spec.satisfies("~nblib"):
             options.append("-DGMX_INSTALL_NBLIB_API=OFF")
         if self.spec.satisfies("~gmxapi"):