Fixed gcc -Wstringop-overflow and -Wdeprecated-declarations.

[AbdallaDalleh]

1st warning:

../seq_mac.c: In function ‘seqMacEval’:
../seq_mac.c:81:5: warning: ‘strncpy’ specified bound depends on the length of the 
source argument [-Wstringop-overflow=]
     strncpy(outStr, value, valLth);
     ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
../seq_mac.c:75:14: note: length computed here
     valLth = strlen(value);

seqMacEval already passes the destination size as the 4th argument maxChar, this is clear in various calls:

• src/seq/seq_main.c:395
• src/seq/seq_if.c:668

2nd warning:

../../../include/seqMain.c: In function ‘main’:
../../../include/seqMain.c:28:9: warning: ‘epicsThreadExitMain’ is deprecated 
[-Wdeprecated-declarations]
         epicsThreadExitMain();

function call has been replaced with a loop+sleep, as the deprecation notice suggest. Similar case exist in test/validate/seqMain.c

[ralphlange]

Careful with the 2nd one:
This probably depends on the version of Base, and the sequencer needs to be working against a whole range...

[ralphlange]

Works fine across Base versions, it seems.