MAGMAmic is a C++ library and it cannot be used with C code directly.
When icc detects that you want to compile .c++ file it automatically switches to icpc (Intel C++ compiler) which in turn results in the above error.
Solution: Either switch to icpc or rename your files to .c++
This question was answered by mark on the MAGMA forums. Link: http://icl.cs.utk.edu/magma/forum/viewtopic.php?f=2&t=1587&p=4442#p4442