Allow setting an arbitary value for blddirffi in testsuite

It is useful when tests are executed not from build directory. So
the path of the build directory may be passed through site.exp or
runtest.

Signed-off-by: Yuriy Kolerov <yuriy.kolerov@synopsys.com>

testsuite/lib/libffi.exp

@@ -102,11 +102,14 @@ proc libffi-init { args } {
     global ld_library_path
     global compiler_vendor
 
-    set blddirffi [pwd]/.. 
+    if ![info exists blddirffi] {
+	set blddirffi [pwd]/..
+    }
+
     verbose "libffi $blddirffi"
 
     # Which compiler are we building with?
-    set tmp [grep ../config.log "^ax_cv_c_compiler_vendor.*$"]
+    set tmp [grep "$blddirffi/config.log" "^ax_cv_c_compiler_vendor.*$"]
     regexp -- {^[^=]*=(.*)$} $tmp nil compiler_vendor
 
     if { [string match $compiler_vendor "gnu"] } {