Missing support for `_Complex`

[Jezurko]

Missing support for ISO C99 _Complex and GNU __complex__ Example benchmarks:

• Regression/C/gcc-c-torture/execute/20010605-2.c
• Regression/C/gcc-c-torture/execute/20010605-2.c
• Regression/C/gcc-c-torture/execute/20030910-1.c
• Regression/C/gcc-c-torture/execute/20050121-1.c
• Regression/C/gcc-c-torture/execute/20070614-1.c
• Regression/C/gcc-c-torture/execute/complex-1.c
• Regression/C/gcc-c-torture/execute/complex-2.c
• Regression/C/gcc-c-torture/execute/complex-4.c
• Regression/C/gcc-c-torture/execute/complex-5.c
• Regression/C/gcc-c-torture/execute/complex-6.c
• Regression/C/gcc-c-torture/execute/complex-7.c
• Regression/C/gcc-c-torture/execute/pr38969.c
• Regression/C/gcc-c-torture/execute/pr42248.c
• Regression/C/gcc-c-torture/execute/pr49644.c
• Benchmarks/Misc/mandel.c
• Benchmarks/Misc/mandel-2.c