configure: set valgrind-memcheck toolchain when --valgrind is specified

This avoids duplicating the default command line arguments
Signed-off-by: Michael Niedermayer <michaelni@gmx.at>

configure

@@ -2493,6 +2493,8 @@ strip_default="${cross_prefix}${strip_default}"
 
 sysinclude_default="${sysroot}/usr/include"
 
+test -n "$valgrind" && toolchain="valgrind-memcheck"
+
 case "$toolchain" in
     clang-asan)
         cc_default="clang"
@@ -4166,7 +4168,6 @@ enabled vdpau &&
 disabled iconv || check_func_headers iconv.h iconv || check_lib2 iconv.h iconv -liconv || disable iconv
 
 enabled debug && add_cflags -g"$debuglevel" && add_asflags -g"$debuglevel"
-test -n "$valgrind" && target_exec="$valgrind --error-exitcode=1 --malloc-fill=0x2a --track-origins=yes --leak-check=full --gen-suppressions=all --suppressions=$source_path/tests/fate-valgrind.supp"
 
 # add some useful compiler flags if supported
 check_cflags -Wdeclaration-after-statement