Don't use strict fortran standard on buggy GCC versions

Author: sethrj

.travis.yml

@@ -10,7 +10,7 @@ matrix:
       sudo: required
       dist: xenial
     - os: linux
-      env: SWIGLANG=fortran GCC=6 CPP14=1
+      env: SWIGLANG=fortran GCC=8 CPP14=1 FCSTD=f2003
       sudo: required
       dist: xenial
     - os: linux

Doc/Manual/src/Fortran.md

@@ -1888,6 +1888,15 @@ void not_wrapped(UnknownType*);
 void should_be_wrapped(UnknownType*);
 ```
 
+## Cross-language polymorphism using directors
+
+Fortran has much less introspection than Java, Python, and other less static
+languages. Therefore director methods can't automatically detect whether the
+target language (Fortran) overrides a particular method.
+
+Note that a bug in GCC prevents versions before 8 from using the
+`--std=f2003` flag (see [GNU bug 84924](https://gcc.gnu.org/bugzilla/show_bug.cgi?id=84924)).
+
 ## Known Issues
 
 A number of known limitations to the SWIG Fortran module are tracked [on

Tools/testflags.py

@@ -65,11 +65,11 @@ def get_cxxflags(language, std, compiler):
     return cxxflags[language]
 
 def get_fcflags(language, std, compiler):
-    if not std:
-        std = "f2003"
-    fcflags = ["-std=" + std, "-Wall", "-Wextra", "-Wimplicit-procedure",
+    fcflags = ["-Wall", "-Wextra", "-Wimplicit-procedure",
             "-Wimplicit-interface", "-Wno-compare-reals",
             "-ffree-line-length-none"]
+    if std:
+        fcflags.append("-std=" + std)
     # The boost version on the systems seems to be compiled as multithreaded
     # but does not link against the pthread library (and I guess the C++
     # compiler does?)