CMakeLists.txt: define APFEL_VERSION, like in config.h.in

[veprbl]

This fixes a crash observed in builds with either -fsanitize=address or -fstack-protector. ASAN is enabled on CI on Linux to help catch such issues. Version reported in the welcome message is corrected along the way.

The issue was that 6 byte apfelversion variable is overwritten with an uninitialized macro "APFEL_VERSION":

==4268==ERROR: AddressSanitizer: stack-buffer-overflow on address 0x7f7b07a00026 at pc 0x7f7bea200176 bp 0x7fff03f0df90 sp 0x7fff03f0d750
WRITE of size 14 at 0x7f7b07a00026 thread T0
    #0 0x7f7bea200175 in __interceptor_strncpy (/lib64/libasan.so.8+0xa7175) (BuildId: 7fcb7759bc17ef47f9682414b6d99732d6a6ab0c)
    #1 0x7f7b09a7196b in getapfelversion_ (/__w/apfel/apfel/BUILD/lib64/libAPFEL.so.0.0.0+0x7196b) (BuildId: 97c5a5b3dd9338763c1a566b1d40726fa5188c3c)
    #2 0x7f7b09a762eb in welcomemessage_ (/__w/apfel/apfel/BUILD/lib64/libAPFEL.so.0.0.0+0x762eb) (BuildId: 97c5a5b3dd9338763c1a566b1d40726fa5188c3c)
    #3 0x7f7b09a9a7b6 in reportparameters_ (/__w/apfel/apfel/BUILD/lib64/libAPFEL.so.0.0.0+0x9a7b6) (BuildId: 97c5a5b3dd9338763c1a566b1d40726fa5188c3c)
    #4 0x7f7b09a8d55c in initializeapfel_ (/__w/apfel/apfel/BUILD/lib64/libAPFEL.so.0.0.0+0x8d55c) (BuildId: 97c5a5b3dd9338763c1a566b1d40726fa5188c3c)
    #5 0x4024fa in main (/__w/apfel/apfel/BUILD/examples/Timing+0x4024fa) (BuildId: b00384fea5f68a2087b87c11453e4a22a286f1b6)
    #6 0x7f7b095f2149 in __libc_start_call_main (/lib64/libc.so.6+0x28149) (BuildId: 788cdd41a15985bf8e0a48d213a46e07d58822df)
    #7 0x7f7b095f220a in __libc_start_main_impl (/lib64/libc.so.6+0x2820a) (BuildId: 788cdd41a15985bf8e0a48d213a46e07d58822df)
    #8 0x402c44 in _start (/__w/apfel/apfel/BUILD/examples/Timing+0x402c44) (BuildId: b00384fea5f68a2087b87c11453e4a22a286f1b6)

Address 0x7f7b07a00026 is located in stack of thread T0 at offset 38 in frame
    #0 0x7f7b09a760bf in welcomemessage_ (/__w/apfel/apfel/BUILD/lib64/libAPFEL.so.0.0.0+0x760bf) (BuildId: 97c5a5b3dd9338763c1a566b1d40726fa5188c3c)

  This frame has 11 object(s):
    [32, 38) 'apfelversion' (line 10) <== Memory access at offset 38 overflows this variable

[scarrazza]

Thank you @veprbl.