Only append compile flags to the link flags when appropriate

We should only append the compiler flags to the link flags when the
compiler is used as a wrapper around the linker during the link process

mesonbuild/environment.py

@@ -701,7 +701,7 @@ class Environment():
         return self.coredata.get_builtin_option('datadir')
 
 
-def get_args_from_envvars(lang):
+def get_args_from_envvars(lang, compiler_is_linker):
     """
     @lang: Language to fetch environment flags for
 
@@ -727,15 +727,21 @@ def get_args_from_envvars(lang):
     link_flags = os.environ.get('LDFLAGS', '')
     log_var('LDFLAGS', link_flags)
     link_flags = link_flags.split()
+    if compiler_is_linker:
+        # When the compiler is used as a wrapper around the linker (such as
+        # with GCC and Clang), the compile flags can be needed while linking
+        # too. This is also what Autotools does. However, we don't want to do
+        # this when the linker is stand-alone such as with MSVC C/C++, etc.
+        link_flags = compile_flags + link_flags
 
     # Pre-processof rlags (not for fortran)
     preproc_flags = ''
     if lang in ('c', 'cpp', 'objc', 'objcpp'):
         preproc_flags = os.environ.get('CPPFLAGS', '')
     log_var('CPPFLAGS', preproc_flags)
-    preproc_flags = preproc_flags.split()
+    compile_flags += preproc_flags.split()
 
-    return (compile_flags + preproc_flags, link_flags + compile_flags)
+    return (compile_flags, link_flags)
 
 class CrossBuildInfo():
     def __init__(self, filename):

mesonbuild/interpreter.py

@@ -1619,8 +1619,11 @@ class Interpreter():
                     else:
                         raise
             mlog.log('Native %s compiler: ' % lang, mlog.bold(' '.join(comp.get_exelist())), ' (%s %s)' % (comp.id, comp.version), sep='')
+            compiler_is_linker = False
+            if hasattr(comp, 'get_linker_exelist'):
+                compiler_is_linker = (comp.get_exelist() == comp.get_linker_exelist())
             if not comp.get_language() in self.coredata.external_args:
-                (ext_compile_args, ext_link_args) = environment.get_args_from_envvars(comp.get_language())
+                (ext_compile_args, ext_link_args) = environment.get_args_from_envvars(comp.get_language(), compiler_is_linker)
                 self.coredata.external_args[comp.get_language()] = ext_compile_args
                 self.coredata.external_link_args[comp.get_language()] = ext_link_args
             self.build.add_compiler(comp)