Win: Restore oneAPI env setup (#50444)

oneAPI env setup was prematurely removed in compilers-as-nodes update
(#45189 - removed from the compiler class but not added to the
associated compiler package): restore it.

var/spack/repos/spack_repo/builtin/packages/msvc/package.py

@@ -158,6 +158,39 @@ def init_msvc(self):
         )
         self.vcvars_call = VCVarsInvocation(vcvars_script_path, arch, msvc_version)
         env_cmds.append(self.vcvars_call)
+
+        def get_oneapi_root(pth: str):
+            """From within a prefix known to be a oneAPI path
+            determine the oneAPI root path from arbitrary point
+            under root
+
+            Args:
+                pth: path prefixed within oneAPI root
+            """
+            if not pth:
+                return ""
+            while os.path.basename(pth) and os.path.basename(pth) != "oneAPI":
+                pth = os.path.dirname(pth)
+            return pth
+
+        if self.fortran:
+            # If this found, it sets all the vars
+            oneapi_root = get_oneapi_root(self.fortran)
+            if not oneapi_root:
+                raise RuntimeError(f"Non-oneAPI Fortran compiler {self.fortran} assigned to MSVC")
+            oneapi_root_setvars = os.path.join(oneapi_root, "setvars.bat")
+            # some oneAPI exes return a version more precise than their
+            # install paths specify, so we determine path from
+            # the install path rather than the fc executable itself
+            numver = r"\d+\.\d+(?:\.\d+)?"
+            pattern = f"((?:{numver})|(?:latest))"
+            version_from_path = re.search(pattern, self.fortran).group(1)
+            oneapi_version_setvars = os.path.join(
+                oneapi_root, "compiler", version_from_path, "env", "vars.bat"
+            )
+            env_cmds.extend(
+                [VarsInvocation(oneapi_version_setvars), VarsInvocation(oneapi_root_setvars)]
+            )
         self.msvc_compiler_environment = CmdCall(*env_cmds)
 
     def _standard_flag(self, *, language: str, standard: str) -> str: