configure.ac: Allow user to disable gflags

cmake: fixed gflags namespace detection (fixes #193)

This commit fixes gflags namespace detection using Intel compiler and ensures
the generated try_compile command line does not produce malformed paths.

cmake: do not hardcode relative install directories

cmake: changed project name from google-glog to glog

Cygwin support

[RFC] reduce heap memory allocations to zero

rate limit calls to posix_fadvise()

Use gflags ALIAS instead of ${gflags_XXX} vars

Port stack tracing to Windows

This method ensure that all users of glog get automatically linked to
the DbgHelp library without needing to set compiler flags.

Necessary when building with BUILD_SHARED_LIBS=1.

The gflags project updated their CMake config last year with a
`gflags` ALIAS target. This can be used instead of the legacy
`${gflags_LIBRARIES}` and `${gflags_INCLUDE_DIRS}` variables. It also
looks cleaner.

Fixes #198

Remove files generated by autotools

closes #165 

for #165. I think not many projects have them in their repo.

Backport internal changes

Don't rely on an internal-linkage extern "C" function having an
unmangled name. This isn't required by the ABI, and in fact is not
valid for a conforming compiler(!). Instead, allow symbolization to
produce either a mangled or an unmangled name here.

CHECK_NOTNULL works with smart pointers when compiled in C++11.

Add __declspec(noreturn) on Win

Currently cl.exe doesn't know LOG(FATAL) exits the program. Set
__declspec(noreturn).

DCHECK_ALWAYS_ON to make D* enabled under NDEBUG

The macro NDEBUG could be automatically defined for release build on
some build environments (e.g. MSVC).  If we use NDEBUG as a key to
distinguish using DCHECK as CHECK (I call this DCHECK is enabled) or
not, we cannot make DCHECK enabled for release build on such
environments.

Considering people use a program with glog for presubmit testing or
dogfooding, they should need to do release build with DCHECK enabled.