Remove */lib paths from m4 (Issu #4095: boinc fails to link with LLD)

BOINC fails to link with LLD because of /usr/lib in the link command
line.

LLD does not continue to search for the correct library, once it
finds one that doesn't fit. This is made by design and will not
change.
See also : https://bugs.gentoo.org/732024

The reason for LLD failing is, that its build system puts -L/usr and
-L/usr/lib into the command line options. While these are not
neccessary at all, they cause LLD to find 32bit libraries on 64bit
systems first. As these 32bit libraries can not be used, LLD errors
out.

This commit removes the superfluous hard-coded injection of -L/usr
and -L/usr/lib into the command line.
The resulting build system has been tested with
* Clang + LLD
* gcc + ld.bfd
* gcc + ld.gold

Bug: #4095
Signed-off-by: Sven Eden <sven.eden@prydeworx.com>

m4/ax_check_gl.m4

@@ -39,7 +39,7 @@ else
       GL_CFLAGS="-I${x_includes} -I${prefix}/include ${GL_CFLAGS}"
     fi
     if test -n "$x_libraries"; then
-      GL_LIBS="-L${x_libraries} -L${prefix}/lib -lX11 ${GL_LIBS}"
+      GL_LIBS="-L${x_libraries} -lX11 ${GL_LIBS}"
     fi
   fi
 
@@ -58,7 +58,7 @@ else
     else
       ax_try_lib="${ax_lib}"
     fi
-    LIBS="-L${prefix}/lib ${ax_try_lib} ${GL_LIBS} ${ax_save_LIBS}"
+    LIBS="${ax_try_lib} ${GL_LIBS} ${ax_save_LIBS}"
     AC_LINK_IFELSE(
     [AC_LANG_PROGRAM([[
 # if HAVE_WINDOWS_H && defined(_WIN32)
@@ -66,7 +66,7 @@ else
 # endif
 # include <GL/gl.h>]],
                      [[glBegin(0)]])],
-    [ax_cv_check_gl_libgl="-L${prefix}/lib ${ax_try_lib}"; break])
+    [ax_cv_check_gl_libgl="${ax_try_lib}"; break])
   done
   LIBS=${ax_save_LIBS}
   CPPFLAGS=${ax_save_CPPFLAGS}])

m4/ax_check_glu.m4

@@ -19,7 +19,7 @@ if test "X${with_apple_opengl_framework}" != "Xyes"; then
     else
       ax_try_lib="${ax_lib}"
     fi
-    LIBS="-L${prefix}/lib ${ax_try_lib} ${GL_LIBS} ${ax_save_LIBS}"
+    LIBS="${ax_try_lib} ${GL_LIBS} ${ax_save_LIBS}"
     #
     # libGLU typically links with libstdc++ on POSIX platforms. However,
     # setting the language to C++ means that test program source is named
@@ -37,7 +37,7 @@ if test "X${with_apple_opengl_framework}" != "Xyes"; then
 # endif
 # include <GL/glu.h>]],
                      [[gluBeginCurve(0)]])],
-    [ax_cv_check_glu_libglu="-L${prefix}/lib ${ax_try_lib}"; break])
+    [ax_cv_check_glu_libglu="${ax_try_lib}"; break])
     if test X$ax_compiler_ms = Xyes; then
       AC_LANG_POP([C])
     fi

m4/ax_check_glut.m4

@@ -41,7 +41,7 @@ else
     else
       ax_try_lib="${ax_lib}"
     fi
-    LIBS="-L${prefix}/lib ${ax_try_lib} ${GLUT_LIBS} ${ax_save_LIBS}"
+    LIBS="${ax_try_lib} ${GLUT_LIBS} ${ax_save_LIBS}"
     AC_LINK_IFELSE(
     [AC_LANG_PROGRAM([[
 #define FREEGLUT_STATIC 1
@@ -50,7 +50,7 @@ else
 # endif
 # include <GL/glut.h>]],
                      [[glutMainLoop()]])],
-    [ax_cv_check_glut_libglut="-L${prefix}/lib ${ax_try_lib}"; break])
+    [ax_cv_check_glut_libglut="${ax_try_lib}"; break])
 
   done
   LIBS=${ax_save_LIBS}

m4/check_ssl.m4

@@ -46,7 +46,7 @@ if test "x${SSL_LIBS}" = "x" ; then
       SSLDIR="${ssldir}"
       SSL_CFLAGS="-I$ssldir/include -I$ssldir/include/openssl";
       SSL_CXXFLAGS="-I$ssldir/include -I$ssldir/include/openssl";
-      SSL_LIBS="-L$ssldir -L$ssldir/lib -lssl -lcrypto"
+      SSL_LIBS="-lssl -lcrypto"
       AC_CHECK_LIB([dl], [dlopen], 
           [SSL_LIBS="${SSL_LIBS} ${sah_lib_last}"])
       AC_CHECK_LIB([z], [gzopen], 
@@ -58,7 +58,7 @@ if test "x${SSL_LIBS}" = "x" ; then
       SSLDIR="${ssldir}"
       SSL_CFLAGS="-I$ssldir/include/"
       SSL_CXXFLAGS="-I$ssldir/include/"
-      SSL_LIBS="-L$ssldir -L$ssldir/lib -lssl -lcrypto"
+      SSL_LIBS="-lssl -lcrypto"
       AC_CHECK_LIB([dl], [dlopen], 
           [SSL_LIBS="${SSL_LIBS} ${sah_lib_last}"])
       AC_CHECK_LIB([z], [gzopen],