Fortran MEX: add -Wimplicit-interface to compiler flags

This warns about hard-to-detect bugs where a function is called with an
implicit interface, thus possibly having mismatches in the calling sequence.

mex/build/matlab/mex.am

@@ -8,7 +8,7 @@ DEFS += -DMATLAB_MEX_FILE
 DEFS += -DMEXEXT=\"$(MEXEXT)\"
 
 AM_CFLAGS = $(MATLAB_CFLAGS) -Wall -Wno-parentheses
-AM_FCFLAGS = $(MATLAB_FCFLAGS) -Wall
+AM_FCFLAGS = $(MATLAB_FCFLAGS) -Wall -Wimplicit-interface
 AM_CXXFLAGS = $(MATLAB_CXXFLAGS) -Wall -Wno-parentheses -Wold-style-cast
 AM_LDFLAGS = $(MATLAB_LDFLAGS)
 LIBS += $(MATLAB_LIBS)

mex/build/octave/mex.am

@@ -6,7 +6,7 @@ DEFS += -DOCTAVE_MEX_FILE
 DEFS += -DMEXEXT=\".mex\"
 
 AM_CFLAGS = $(shell $(MKOCTFILE) -p CPICFLAG) -Wall -Wno-parentheses
-AM_FCFLAGS = $(shell $(MKOCTFILE) -p FPICFLAG) -Wall
+AM_FCFLAGS = $(shell $(MKOCTFILE) -p FPICFLAG) -Wall -Wimplicit-interface
 AM_CXXFLAGS = $(shell $(MKOCTFILE) -p CXXPICFLAG) -Wall -Wno-parentheses -Wold-style-cast
 AM_LDFLAGS = $(shell $(MKOCTFILE) -p DL_LDFLAGS) -L"$(shell $(MKOCTFILE) -p OCTLIBDIR)"