Fix MSVC backend crashes when `c_pch` or `cpp_pch` is not an array

mesonbuild/backend/vs2010backend.py

@@ -862,7 +862,14 @@ class Vs2010Backend(backends.Backend):
             if not pch:
                 continue
             pch_node.text = 'Use'
+            if compiler.id == 'msvc':
+                if len(pch) != 2:
+                    raise RuntimeError('MSVC requires one header and one source to produce precompiled headers.')
                 pch_sources[lang] = [pch[0], pch[1], lang]
+            else:
+                # I don't know whether its relevant but let's handle other compilers
+                # used with a vs backend
+                pch_sources[lang] = [pch[0], None, lang]
         if len(pch_sources) == 1:
             # If there is only 1 language with precompiled headers, we can use it for the entire project, which
             # is cleaner than specifying it for each source file.
@@ -1017,6 +1024,7 @@ class Vs2010Backend(backends.Backend):
                 self.add_include_dirs(lang, inc_cl, file_inc_dirs)
             for lang in pch_sources:
                 header, impl, suffix = pch_sources[lang]
+                if impl:
                     relpath = os.path.join(proj_to_src_dir, impl)
                     inc_cl = ET.SubElement(inc_src, 'CLCompile', Include=relpath)
                     pch = ET.SubElement(inc_cl, 'PrecompiledHeader')