look for static Boost libraries on *nix when requested

This was already mostly working before due to how the linker arguments were constructed, but this will now be more resilient to the case where dynamic libraries only are present.

mesonbuild/dependencies/misc.py

@@ -203,7 +203,9 @@ class BoostDependency(Dependency):
             self.lib_modules_mt[modname] = fname
 
     def detect_lib_modules_nix(self):
-        if mesonlib.is_osx() and not self.want_cross:
+        if self.static:
+            libsuffix = 'a'
+        elif mesonlib.is_osx() and not self.want_cross:
             libsuffix = 'dylib'
         else:
             libsuffix = 'so'
@@ -221,7 +223,7 @@ class BoostDependency(Dependency):
                 name = lib.split('.')[0].split('_', 1)[-1]
                 # I'm not 100% sure what to do here. Some distros
                 # have modules such as thread only as -mt versions.
-                if entry.endswith('-mt.so'):
+                if entry.endswith('-mt.{}'.format(libsuffix)):
                     self.lib_modules_mt[name] = True
                 else:
                     self.lib_modules[name] = True