Try to make build more robust

Mixing Python and EPICS build systems has become a rather tangled web.
Here we take two precautions: first, sanitise our #defines before including
Python.h, and second, only using the flags we absolutely need from
`python-config --cflags`.

Author: Araneidae

softIocApp/Makefile

@@ -28,7 +28,10 @@ PYTHON_LIB_DIR := $(shell $(PYTHON) -c \
 
 USR_CFLAGS += -std=gnu99 -Werror
 
-USR_CFLAGS += $(shell $(PYTHON_CONFIG) --cflags)
+# We just want the include path for the python library, that should be enough.
+# There are a lot of other settings which may conflict with EPICS build
+# settings, so we omit them.
+USR_CFLAGS += $(shell $(PYTHON_CONFIG) --cflags | tr ' '  '\n' | grep '^-I')
 
 # This tells the compiler to ignore errors generated by EPICS includes.  We need
 # this because the EPICS headers have non strict prototypes in places.

softIocApp/PythonSupport.c

@@ -1,3 +1,6 @@
+/* See note in softMain.c about these #undefs. */
+#undef _POSIX_C_SOURCE
+#undef _XOPEN_SOURCE
 #include <Python.h>
 #include <string.h>