openfoam: disable FPE handling for Fujitsu compiler (#21769)

- as outlined in merge-request #21336 some clang compilers
  can trigger erroneous floating point exceptions.

  OpenFOAM normally traps FPE, but disable this in the etc/controlDict
  for specific compilers:

      change "trapFpe digit;" -> "trapFpe 0;"

  Eliminate previous use of FOAM_SGIFPE env variable in favour of
  using the etc/controlDict setting - cleaner and robuster.

Co-authored-by: Mark Olesen <Mark.Olesen@esi-group.com>

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

@@ -405,10 +405,7 @@ def setup_minimal_environment(self, env):
     def setup_build_environment(self, env):
         """Sets the build environment (prior to unpacking the sources).
         """
-        # Avoid the exception that occurs at runtime
-        # when building with the Fujitsu compiler.
-        if self.spec.satisfies('%fj'):
-            env.set('FOAM_SIGFPE', 'false')
+        pass
 
     def setup_run_environment(self, env):
         """Sets the run environment (post-installation).
@@ -549,6 +546,16 @@ def patch(self):
                     rcfile,
                     backup=False)
 
+    def configure_trapFpe_off(self):
+        """Disable trapFpe handling.
+        Seems to be needed for several clang-derivatives.
+        """
+        # Set 'trapFpe 0' in etc/controlDict
+        controlDict = 'etc/controlDict'
+        if os.path.exists(controlDict):
+            filter_file(r'trapFpe\s+\d+\s*;', 'trapFpe 0;',
+                        controlDict, backup=False)
+
     @when('@1812: %fj')
     @run_before('configure')
     def make_fujitsu_rules(self):
@@ -560,6 +567,7 @@ def make_fujitsu_rules(self):
         arch_rules = 'wmake/rules/linuxARM64'  # self.arch
         src = arch_rules + 'Clang'
         dst = arch_rules + 'Fujitsu'  # self.compiler
+        self.configure_trapFpe_off()  # LLVM may falsely trigger FPE
 
         if os.path.exists(dst):
             return