(almost) silent creation of static lib instead of dynamic linked lib

[Evgeny Grin]

Hi!

Libtool always build static lib if dynamic lib can't be created.
This behavior is inconsistent with other build tools. For example if GCC can't 
compile something, it fail with error.
If I need a shared lib, this doesn't mean that static lib will satisfy me.
When I run configure with "--enable-shared" (or shared enabled by default), I 
expect that "make" will build shared lib or fail with error.
Currently developers are forced to check "make" return code and additionally 
check for real presence of shared lib files.
I think that static lib must be built only if requested and shared lib must be 
built when it's requested.
I suggest to add new default configure switches "--enable-static=auto" and 
"--enable-shared=auto". If both are auto then libtool will try to make both 
static and shared and fail only if both static/shared can't be built. If any of 
static/shared are explicitly requested, libtool must fail if corresponding 
static/shared can't be built.

Best Wishes,
Evgeny