Use case-insensitive suffix check for fortran

In Fortran it is common to use capital F in the suffix (eg. '.F90') if
the source file makes use of preprocessor statements. Such files should
probably be treated like all other fortran files by meson.

Case insensitivity for suffixes was already implemented several places
in meson before this. So most likely, the few places changed here were
oversights anyway.

mesonbuild/backend/ninjabackend.py

@@ -637,7 +637,7 @@ int dummy;
         if self.environment.is_llvm_ir(source) or \
            self.environment.is_assembly(source):
             return False
-        suffix = os.path.splitext(source)[1][1:]
+        suffix = os.path.splitext(source)[1][1:].lower()
         for lang in self.langs_cant_unity:
             if lang not in target.compilers:
                 continue
@@ -925,7 +925,7 @@ int dummy;
         all_suffixes = set(compilers.lang_suffixes['cpp']) | set(compilers.lang_suffixes['fortran'])
         selected_sources = []
         for source in compiled_sources:
-            ext = os.path.splitext(source)[1][1:]
+            ext = os.path.splitext(source)[1][1:].lower()
             if ext in all_suffixes:
                 selected_sources.append(source)
         return selected_sources

mesonbuild/scripts/depscan.py

@@ -46,7 +46,7 @@ class DependencyScanner:
         self.sources_with_exports = [] # type: T.List[str]
 
     def scan_file(self, fname: str) -> None:
-        suffix = os.path.splitext(fname)[1][1:]
+        suffix = os.path.splitext(fname)[1][1:].lower()
         if suffix in lang_suffixes['fortran']:
             self.scan_fortran_file(fname)
         elif suffix in lang_suffixes['cpp']:
@@ -131,7 +131,7 @@ class DependencyScanner:
         return objname
 
     def module_name_for(self, src: str) -> str:
-        suffix= os.path.splitext(src)[1][1:]
+        suffix = os.path.splitext(src)[1][1:].lower()
         if suffix in lang_suffixes['fortran']:
             exported = self.exports[src]
             # Module foo:bar goes to a file name foo@bar.smod