[PATCH v6 09/12] Add symbolic execution support.

Gives an opportunity to execute the code on bit level, assigning
symbolic values to the variables which don't have initial values.
Supports only CRC specific operations.

Example:

uint8_t crc;
uint8_t pol = 1;
crc = crc ^ pol;

during symbolic execution crc's value will be:
crc(8), crc(7), ... crc(1), crc(0) ^ 1

gcc/
	* Makefile.in (OBJS): Add sym-exec/sym-exec-expression.o,
	sym-exec/sym-exec-state.o, sym-exec/sym-exec-condition.o.
	* configure (sym-exec): New subdir.
	* sym-exec/sym-exec-condition.cc: New file.
	* sym-exec/sym-exec-condition.h: New file.
	* sym-exec/sym-exec-expr-is-a-helper.h: New file.
	* sym-exec/sym-exec-expression.cc: New file.
	* sym-exec/sym-exec-expression.h: New file.
	* sym-exec/sym-exec-state.cc: New file.
	* sym-exec/sym-exec-state.h: New file.

Co-authored-by: Mariam Arutunian <mariamarutunian@gmail.com>