dependencies/boost: Fix 32-bit vs 64-bit on Windows

Fixes https://github.com/mesonbuild/meson/issues/526

Also removes useless and incorrect mesonlib.is_32bit() function. We
cannot trust that the architecture that Python is built for is the same
as the one we're targetting.

mesonbuild/dependencies.py

@@ -25,6 +25,7 @@ import sysconfig
 from . mesonlib import MesonException
 from . import mlog
 from . import mesonlib
+from .environment import detect_cpu_family
 
 class DependencyException(MesonException):
     def __init__(self, *args, **kwargs):
@@ -582,11 +583,21 @@ class BoostDependency(Dependency):
         return self.detect_lib_modules_nix()
 
     def detect_lib_modules_win(self):
-        if mesonlib.is_32bit():
+        arch = detect_cpu_family(self.environment.coredata.compilers)
+        # Guess the libdir
+        if arch == 'x86':
             gl = 'lib32*'
-        else:
+        elif arch == 'x86_64':
             gl = 'lib64*'
+        else:
+            # Does anyone do Boost cross-compiling to other archs on Windows?
+            gl = None
+        # See if the libdir is valid
+        if gl:
             libdir = glob.glob(os.path.join(self.boost_root, gl))
+        else:
+            libdir = []
+        # Can't find libdir, bail
         if len(libdir) == 0:
             return
         libdir = libdir[0]

mesonbuild/mesonlib.py

@@ -91,9 +91,6 @@ def is_windows():
     platname = platform.system().lower()
     return platname == 'windows' or 'mingw' in platname
 
-def is_32bit():
-    return not(sys.maxsize > 2**32)
-
 def is_debianlike():
     return os.path.isfile('/etc/debian_version')