Always catch PermissionError while looking for Ninja

Also convert a few other generic `except Exception`s to be more specific

Closes #1088

mesonbuild/dependencies.py

@@ -233,7 +233,7 @@ class PkgConfigDependency(Dependency):
                              '(%s)' % out.decode().strip())
                 PkgConfigDependency.pkgconfig_found = True
                 return
-        except Exception:
+        except (FileNotFoundError, PermissionError):
             pass
         PkgConfigDependency.pkgconfig_found = False
         if not self.silent:
@@ -358,7 +358,7 @@ class WxDependency(Dependency):
                     self.wxc = wxc
                     WxDependency.wx_found = True
                     return
-            except Exception:
+            except (FileNotFoundError, PermissionError):
                 pass
         WxDependency.wxconfig_found = False
         mlog.log('Found wx-config:', mlog.red('NO'))
@@ -1040,7 +1040,7 @@ class GnuStepDependency(Dependency):
             gp = subprocess.Popen([confprog, '--help'],
                                   stdout=subprocess.PIPE, stderr=subprocess.PIPE)
             gp.communicate()
-        except FileNotFoundError:
+        except (FileNotFoundError, PermissionError):
             self.args = None
             mlog.log('Dependency GnuStep found:', mlog.red('NO'), '(no gnustep-config)')
             return

mesonbuild/environment.py

@@ -43,7 +43,8 @@ def detect_ninja():
     for n in ['ninja', 'ninja-build']:
         try:
             p = subprocess.Popen([n, '--version'], stdout=subprocess.PIPE, stderr=subprocess.DEVNULL)
-        except FileNotFoundError:
+        except (FileNotFoundError, PermissionError):
+            # Doesn't exist in PATH or isn't executable
             continue
         version = p.communicate()[0].decode(errors='ignore')
         # Perhaps we should add a way for the caller to know the failure mode