enable out of source builds

The changes should be GNU-Make / Autotools compatible. On the machines I have access to they enable out of source builds, for instance :

mculpo@nuvolari:~/epfl/swift$ tree -d -L 2
.
├── build
│   ├── doc
│   ├── examples
│   ├── src
│   └── tests
├── install
│   ├── bin
│   ├── include
│   └── lib
└── sources
    ├── autom4te.cache
    ├── doc
    ├── examples
    ├── m4
    ├── src
    ├── tests
    └── theory

It enables having different build configurations pointing at the same source checkout.

Status changed to merged

mentioned in commit abaf180f

@pdraper Sorry, I just noticed I didn't update the unit test folder see bf8162e5.

Is it normal that make check fails with :

mpicc -std=gnu99 -DHAVE_CONFIG_H -I. -I../../sources/tests -I..    -I../../sources/src -I/usr/include -DTIMER -O3 -fomit-frame-pointer -malign-double -fstrict-aliasing -ffast-math -march=core-avx2 -mavx2  -Wall -Werror -MT testReading.o -MD -MP -MF .deps/testReading.Tpo -c -o testReading.o ../../sources/tests/testReading.c
../../sources/tests/testReading.c: In function ‘main’:
../../sources/tests/testReading.c:42:18: error: too few arguments to function ‘read_ic_single’
                  0);
                  ^
In file included from ../../sources/src/swift.h:50:0,
                 from ../../sources/tests/testReading.c:24:
../../sources/src/single_io.h:32:6: note: declared here
 void read_ic_single(char* fileName, double dim[3], struct part** parts,
      ^

?

No, looks like an error has crept in. I'll push a fix for that.

Hmm, seems that a number of the unit tests have location issues finding scripts and data files. Those will need to be worked through as well. If you make a new merge request I will accept these two changes and we can create an issue to fix up the tests themselves.

mentioned in merge request !199 (merged)

mentioned in commit 9e88fc31