scripts/populate: properly locate the sysroot and required tools

This fixes two problems:
- the sysroot might be in a sub-directory (think SYSROOT_DIR_PREFIX)
- it is not needed to have the target tuple to properly detect the sysroot
  and the required tools

As a side effect, this script is now no longer dependent on the target
tuple, and in the future, we might be able to share it across many
toolchains (when/if we can install all of them in the same place).

scripts/populate.in

@@ -4,20 +4,32 @@
 # Licensed under the GPL v2
 set -e
 
-# Detect where the toolchain is:
-CT_PREFIX_DIR="$(cd "$(dirname "$0")/.."; pwd)"
-CT_BIN_DIR="${CT_PREFIX_DIR}/bin"
-CT_READELF="${CT_BIN_DIR}/@@CT_TARGET@@-readelf"
-CT_LIB_DIR="${CT_PREFIX_DIR}/lib"
-CT_SYSROOT_DIR="$(cd "${CT_BIN_DIR}/../@@CT_TARGET@@/sys-root"; pwd)"
-
-myname=$(basename "$0")
-
 # Use the tools discovered by crosstool-NG's ./configure:
 install="@@CT_install@@"
 grep="@@CT_grep@@"
 sed="@@CT_sed@@"
 
+# Detect where the toolchain is:
+CT_PREFIX_DIR="$(cd "$(dirname "$0")/.."; pwd)"
+CT_GCC="${0%-populate}-gcc"
+CT_READELF="${0%-populate}-readelf"
+CT_CFG_PREFIX_DIR="$("${CT_GCC}" -v 2>&1            \
+                     |tr ' ' '\n'                   \
+                     |"${grep}" -E -- '--prefix='   \
+                     |cut -d = -f 2-
+                    )"
+CT_CFG_SYSROOT_DIR="$("${CT_GCC}" -v 2>&1                   \
+                      |tr ' ' '\n'                          \
+                      |"${grep}" -E -- '--with-sysroot='    \
+                      |cut -d = -f 2-
+                     )"
+CT_SYSROOT_DIR="$(echo "${CT_CFG_SYSROOT_DIR}"                                  \
+                  |"${sed}" -r -e "s:^${CT_CFG_PREFIX_DIR}:${CT_PREFIX_DIR}:;"  \
+                  |"${sed}" -r -e 's,/+,/,g;'                                   \
+                 )"
+
+myname=$(basename "$0")
+
 doHelp() {
     cat <<_EOF_
 NAME