Code contains C99-style comments, but build system invokes GCC in ANSI C (C90) mode

[adamnovak]

The code here contains comments that begin with //. The Makefile contains the -ansi flag for GCC, which specifies the C90 standard, which does not include such comments. GCC 4.9.0, when invoked in ANSI mode, interprets // as a pair of division operators in a row, and thus predictably fails to build the code.

This issue breaks the build of progressiveCactus on GCC 4.9.0.

This issue can be worked around by adding -std=c99 to the CFLAGS environment variable before building the code.