Do not cache found programs because it is unreliable. Closes #374.

mesonbuild/coredata.py

@@ -154,7 +154,6 @@ class CoreData():
         self.compilers = {}
         self.cross_compilers = {}
         self.deps = {}
-        self.ext_progs = {}
         self.modules = {}
 
     def init_builtins(self, options):

mesonbuild/interpreter.py

@@ -1497,14 +1497,12 @@ class Interpreter():
         if not isinstance(required, bool):
             raise InvalidArguments('"required" argument must be a boolean.')
         exename = args[0]
-        if exename in self.coredata.ext_progs and\
-           self.coredata.ext_progs[exename].found():
-            return ExternalProgramHolder(self.coredata.ext_progs[exename])
         # Search for scripts relative to current subdir.
+        # Do not cache found programs because find_program('foobar')
+        # might give different results when run from different source dirs.
         search_dir = os.path.join(self.environment.get_source_dir(), self.subdir)
         extprog = dependencies.ExternalProgram(exename, search_dir=search_dir)
         progobj = ExternalProgramHolder(extprog)
-        self.coredata.ext_progs[exename] = extprog
         if required and not progobj.found():
             raise InvalidArguments('Program "%s" not found.' % exename)
         return progobj