Build system bugs related to handling of 'LIBS' environment variable

Hello,

Git fails to build if LIBS contains -lpthread.  To reproduce:

  export LIBS=-lpthread
  ./configure
  make V=1 git-credential-store

The bug is that linker command line does not contain -lpthread, so linking fails.

configure respects LIBS and finds that it does not have to add anything for pthread:

checking for POSIX Threads with ''... yes

But (first bug) configure does not pass the LIBS variable in config.mak.autogen. Even if it did, Makefile would overwrite (second bug) LIBS with:

  LIBS = $(GITLIBS) $(EXTLIBS)

Makefile should rather append to LIBS.

Dmitri Gribenko

-- main(i,j){for(i=2;;i++){for(j=2;j<i;j++){if(!(i%j)){j=0;break;}}if (j){printf("%d\n",i);}}} /*Dmitri Gribenko <gribozavr@gmail.com>*/