add pre+post prepare hooks for LLVM to solve A64FX build issue

Author: bedroge

eb_hooks.py

@@ -736,6 +736,28 @@ def post_prepare_hook_highway_handle_test_compilation_issues(self, *args, **kwar
                 update_build_option('optarch', self.orig_optarch)
 
 
+def pre_prepare_hook_llvm_a64fx(self, *args, **kwargs):
+    """
+    Solve issues with compiling LLVM on A64FX by changing the optarch build option.
+    cfr. https://github.com/EESSI/software-layer/issues/1213
+    """
+    cpu_target = get_eessi_envvar('EESSI_SOFTWARE_SUBDIR')
+    if self.name == 'LLVM' and self.version == '15.0.5' and cpu_target == CPU_TARGET_A64FX:
+        self.orig_optarch = build_option('optarch')
+        update_build_option('optarch', 'march=armv8.2-a')
+    else:
+        raise EasyBuildError("LLVM-specific hook triggered for non-Highway easyconfig?!")
+
+
+def post_prepare_hook_llvm_a64fx(self, *args, **kwargs):
+    """
+    Post-prepare hook for LLVM to reset optarch build option.
+    """
+    cpu_target = get_eessi_envvar('EESSI_SOFTWARE_SUBDIR')
+    if self.name == 'LLVM' and self.version == '15.0.5' and cpu_target == CPU_TARGET_A64FX:
+        update_build_option('optarch', self.orig_optarch)
+
+
 def pre_configure_hook(self, *args, **kwargs):
     """Main pre-configure hook: trigger custom functions based on software name."""
     if self.name in PRE_CONFIGURE_HOOKS:
@@ -1610,11 +1632,13 @@ def post_easyblock_hook(self, *args, **kwargs):
 
 PRE_PREPARE_HOOKS = {
     'Highway': pre_prepare_hook_highway_handle_test_compilation_issues,
+    'LLVM': pre_prepare_hook_llvm_a64fx,
 }
 
 POST_PREPARE_HOOKS = {
     'GCCcore': post_prepare_hook_gcc_prefixed_ld_rpath_wrapper,
     'Highway': post_prepare_hook_highway_handle_test_compilation_issues,
+    'LLVM': post_prepare_hook_llvm_a64fx,
 }
 
 PRE_CONFIGURE_HOOKS = {