Syntax check generated headers using both C and C++ compilers

For C++ tests, check header compilation using C++ compiler too, as this
detects constructs valid in C but invalid in C++ and will also be useful
for checking C++-specific parts of the headers that will be generated in
the future.

Examples/Makefile.in

@@ -1363,8 +1363,6 @@ C_LDSHARED = @C_LDSHARED@
 CXX_LDSHARED = @CXX_LDSHARED@
 C_SO = @C_SO@
 
-SYNTAX_CHECK := $(CC) -fsyntax-only -x c
-
 c: $(SRCDIR_SRCS)
 	$(SWIG) -c $(SWIGOPT) -o $(ISRCS) $(INTERFACEPATH)
 	$(CC) -c $(CCSHARED) -I$(SRCDIR) $(CFLAGS) $(ISRCS) $(SRCDIR_SRCS) $(INCLUDES)
@@ -1385,9 +1383,14 @@ $(eval c_compile: c_compile_$(RUNME_EXT))
 
 # This target is used for the unit tests: if we don't have any test code to
 # run, we at least can check that the generated header can be included without
-# giving any syntax errors.
-c_syntax_check:
-	$(SYNTAX_CHECK) -I$(SRCDIR)$(INTERFACEDIR) $(C_HEADER)
+# giving any syntax errors, both when compiling it as C and C++ code.
+c_syntax_check: c_syntax_check_c c_syntax_check_cxx
+
+c_syntax_check_c:
+	$(CC) -fsyntax-only -x c -I$(SRCDIR)$(INTERFACEDIR) $(C_HEADER)
+
+c_syntax_check_cxx:
+	$(CXX) -fsyntax-only -x c++ -I$(SRCDIR)$(INTERFACEDIR) $(C_HEADER)
 
 # -----------------------------------------------------------------
 # Run C example

Examples/test-suite/c/Makefile.in

@@ -117,12 +117,20 @@ endef
 %.cpptest: 
 	$(setup)
 	+(cd $* && $(swig_and_compile_cpp))
-	$(run_testcase)
+	+if [ $(call has_runme,$*) ]; then \
+	  $(do_run_testcase); \
+	else \
+	  cd $* && $(call syntax_check_testcase,$*); \
+	fi
 
 %.ctest:
 	$(setup)
 	+(cd $* && $(swig_and_compile_c))
-	$(run_testcase)
+	+if [ $(call has_runme,$*) ]; then \
+	  $(do_run_testcase); \
+	else \
+	  cd $* && $(call syntax_check_testcase,$*,_c); \
+	fi
 
 %.multicpptest: 
 	$(setup)
@@ -147,12 +155,15 @@ setup = \
 	fi;
 
 # Checks the header syntax if there is no runnable testcase for it.
+#
+# The optional second argument can be "_c" to check syntax using C compiler only
+# (by default both C and C++ compilers are used).
 syntax_check_testcase = \
 	$(MAKE) -f $(top_builddir)/$(EXAMPLES)/Makefile \
 	  SRCDIR='$(SRCDIR)' \
 	  INTERFACEDIR='$(INTERFACEDIR)' \
 	  C_HEADER=$1_wrap.h \
-	  c_syntax_check
+	  c_syntax_check$2
 
 # Compiles C files then runs the testcase unconditionally.
 do_run_testcase = \
@@ -163,15 +174,6 @@ do_run_testcase = \
 	  TARGET='$*' \
 	  c_run
 
-# Only compile and run testcase if we have a runme for it, otherwise only check
-# the syntax of the generated files.
-run_testcase = \
-	+if [ $(call has_runme,$*) ]; then \
-	  $(do_run_testcase); \
-	else \
-	  cd $* && $(call syntax_check_testcase,$*); \
-	fi
-
 # Clean: remove testcase directories
 %.clean:
 	@if [ -d $* ]; then \