Fix gcc compile warning
Clean up some more sign-compare issues

The only known problems left are in files imported from gtkwave,
if not for them you could turn on -Wsign-compare.

Assumes c99 for c code, so the scope of for-loop indexes can be made sane.
C99 is now required for C files.
Fix for GitHub issue #30 : failed assertion in eval_tree.cc

The root cause was the constant propagation done during elaboration
of a multiply operation, which didn't check for mixed real/logic
expressions.
Fix a few cppcheck warnings.
Remove some cppcheck warnings
Some more cppcheck cleanup/updates
vlog95: Note that casex (==?) and casez (synthesis) operators are not supported
Add support for power operator in eval_const()
Fuss with C function prototypes

119 formal void parameters added to keep -Wstrict-prototypes happy.
Process found one real missing prototype in vpi/vcd_priv.h:
EXTERN void vcd_names_delete(struct vcd_names_list_s*tab);
8 such warnings left, all in Tony's code
Update LXT2 files from GTKWave
More fussing with C function prototypes

Six more -Wstrict-prototypes updates that I missed on the first pass.
The remaining warnings of this type originate in the lz4 code base.
Rearrange compiler warning flags

Before this patch, WARNING_FLAGS applied to both C and C++,
and WARNING_FLAGS_CXX applied to C++ only.
This patch adds a WARNING_FLAGS_CC that applies to C only.
That change should be generally useful; in particular the C
code is almost ready for -Wstrict-prototypes, which does not
apply to C++.

-Wextra (or -W) used to only apply to C++ via WARNING_FLAGS_CXX.
This patch moves it to WARNING_FLAGS, to apply to both C and C++.
Unfortunately, that triggers a ton of warnings.

For now, cover most of the new warnings up by adding
-Wno-unused -Wno-sign-compare -Wno-type-limits
to WARNING_FLAGS_CC.  In the long run, I want to change the C coding
style, and take off these disable-warning flags.  But those changes
can dribble in as separate commits; this patch is big enough already.

Actually fix a couple missing-field-initializers in libveriuser/veriusertfs.c.
Remove the unused parameter warnings in tgt-vlog
Fully initialize a couple structures

Caused missing-field-initializers warnings from clang, but
surprisingly not from gcc.
Remove warnings and -Wno-type-limits option since it is not always supported.
Remove missing parameter warnings
Update fst and lxt files to latest from GTKWave also update cppcheck file
Another update of fstapi.c from GTKWave to fix compile warnings.
Eliminate a few more easy warnings

Testing with 32-bit clang 3.3, with additional compiler flags
 -Wsign-compare -Wundef
this patch eliminates the following warnings:

config.h:100:6: warning: 'UINT64_T_AND_ULONG_SAME' is not defined, evaluates to 0 [-Wundef]
vcd_priv2.cc:233:12: warning: duplicate 'extern' declaration specifier [-Wduplicate-decl-specifier]
parse.cc:6496:9: warning: comparison of 0 <= unsigned expression is always true [-Wtautological-compare]
parse.cc:6499:13: warning: comparison of 0 <= unsigned expression is always true [-Wtautological-compare]
parse.cc:6502:9: warning: comparison of 0 <= unsigned expression is always true [-Wtautological-compare]
parse.cc:6510:53: warning: comparison of integers of different signs: 'const unsigned int' and 'int' [-Wsign-compare]

Changing the vlltype elements from unsigned to int reconciles their
type with the native bison YYLTYPE structure.