compilers: Reduce sizes of MSVC linked binaries

- For optimization=s add /O1: Use Maximum Optimization (Favor Size),
  and remove /Os as it's implied by /O1.
- Because we add /O1, this implies /Gy, i.e. Function-Level Linking, so
  unused code can be omitted.
- Add /Gw: Optimize Global Data, so unused data can be omitted.

With buildtype=minsize on x86 this reduces the size of a statically
linked Vala compiler binary from 5 MB down to just 1.87 MB.

mesonbuild/compilers/c.py

@@ -1247,7 +1247,10 @@ class VisualStudioCCompiler(CCompiler):
         return ['/MDd']
 
     def get_buildtype_args(self, buildtype):
-        return compilers.msvc_buildtype_args[buildtype]
+        args = compilers.msvc_buildtype_args[buildtype]
+        if version_compare(self.version, '<18.0'):
+            args = [arg for arg in args if arg != '/Gw']
+        return args
 
     def get_buildtype_linker_args(self, buildtype):
         return compilers.msvc_buildtype_linker_args[buildtype]

mesonbuild/compilers/compilers.py

@@ -145,8 +145,8 @@ arm_buildtype_args = {'plain': [],
 msvc_buildtype_args = {'plain': [],
                        'debug': ["/ZI", "/Ob0", "/Od", "/RTC1"],
                        'debugoptimized': ["/Zi", "/Ob1"],
-                       'release': ["/Ob2"],
-                       'minsize': ["/Zi", "/Ob1"],
+                       'release': ["/Ob2", "/Gw"],
+                       'minsize': ["/Zi", "/Gw"],
                        }
 
 apple_buildtype_linker_args = {'plain': [],
@@ -267,7 +267,7 @@ msvc_optimization_args = {'0': [],
                           '1': ['/O1'],
                           '2': ['/O2'],
                           '3': ['/O3'],
-                          's': ['/Os'],
+                          's': ['/O1'], # Implies /Os.
                           }
 
 clike_debug_args = {False: [],