bootstrap: Detect known C/C++ compiler toolchains

Look for a C/C++ compiler pair from known toolchains on some platforms.
This makes it less likely that mismatched compilers will be found.
Check only if the environment variables CC and CXX are both empty.

bootstrap

@@ -650,11 +650,74 @@ if ${cmake_system_haiku}; then
   cmake_ld_flags="${LDFLAGS} -lroot -lbe"
 fi
 
+#-----------------------------------------------------------------------------
+# Detect known toolchains on some platforms.
+cmake_toolchains=''
+case "${cmake_system}" in
+  *AIX*)   cmake_toolchains='XL GNU' ;;
+  *CYGWIN*) cmake_toolchains='GNU' ;;
+  *Darwin*) cmake_toolchains='GNU Clang' ;;
+  *Linux*) cmake_toolchains='GNU Clang XL PGI PathScale' ;;
+  *MINGW*) cmake_toolchains='GNU' ;;
+esac
+
+# Toolchain compiler name table.
+cmake_toolchain_Clang_CC='clang'
+cmake_toolchain_Clang_CXX='clang++'
+cmake_toolchain_GNU_CC='gcc'
+cmake_toolchain_GNU_CXX='g++'
+cmake_toolchain_PGI_CC='pgcc'
+cmake_toolchain_PGI_CXX='pgCC'
+cmake_toolchain_PathScale_CC='pathcc'
+cmake_toolchain_PathScale_CXX='pathCC'
+cmake_toolchain_XL_CC='xlc'
+cmake_toolchain_XL_CXX='xlC'
+
+cmake_toolchain_try()
+{
+  tc="$1"
+  TMPFILE=`cmake_tmp_file`
+
+  eval "tc_CC=\${cmake_toolchain_${tc}_CC}"
+  echo 'int main() { return 0; }' > "${TMPFILE}.c"
+  cmake_try_run "$tc_CC" "" "${TMPFILE}.c" >> cmake_bootstrap.log 2>&1
+  tc_result_CC="$?"
+  rm -f "${TMPFILE}.c"
+  test "${tc_result_CC}" = "0" || return 1
+
+  eval "tc_CXX=\${cmake_toolchain_${tc}_CXX}"
+  echo 'int main() { return 0; }' > "${TMPFILE}.cpp"
+  cmake_try_run "$tc_CXX" "" "${TMPFILE}.cpp" >> cmake_bootstrap.log 2>&1
+  tc_result_CXX="$?"
+  rm -f "${TMPFILE}.cpp"
+  test "${tc_result_CXX}" = "0" || return 1
+
+  cmake_toolchain="$tc"
+}
+
+cmake_toolchain_detect()
+{
+  cmake_toolchain=
+  for tc in ${cmake_toolchains}; do
+    echo "Checking for $tc toolchain" >> cmake_bootstrap.log 2>&1
+    cmake_toolchain_try "$tc" &&
+    echo "Found $tc toolchain" &&
+    break
+  done
+}
+
+if [ -z "${CC}" -a -z "${CXX}" ]; then
+  cmake_toolchain_detect
+fi
+
+#-----------------------------------------------------------------------------
 # Test C compiler
 cmake_c_compiler=
 
 # If CC is set, use that for compiler, otherwise use list of known compilers
-if [ -n "${CC}" ]; then
+if [ -n "${cmake_toolchain}" ]; then
+  eval cmake_c_compilers="\${cmake_toolchain_${cmake_toolchain}_CC}"
+elif [ -n "${CC}" ]; then
   cmake_c_compilers="${CC}"
 else
   cmake_c_compilers="${CMAKE_KNOWN_C_COMPILERS}"
@@ -697,13 +760,16 @@ See cmake_bootstrap.log for compilers attempted.
 fi
 echo "C compiler on this system is: ${cmake_c_compiler} ${cmake_c_flags}"
 
+#-----------------------------------------------------------------------------
 # Test CXX compiler
 cmake_cxx_compiler=
 
 # On Mac OSX, CC is the same as cc, so make sure not to try CC as c++ compiler.
 
 # If CC is set, use that for compiler, otherwise use list of known compilers
-if [ -n "${CXX}" ]; then
+if [ -n "${cmake_toolchain}" ]; then
+  eval cmake_cxx_compilers="\${cmake_toolchain_${cmake_toolchain}_CXX}"
+elif [ -n "${CXX}" ]; then
   cmake_cxx_compilers="${CXX}"
 else
   cmake_cxx_compilers="${CMAKE_KNOWN_CXX_COMPILERS}"
@@ -754,6 +820,7 @@ See cmake_bootstrap.log for compilers attempted."
 fi
 echo "C++ compiler on this system is: ${cmake_cxx_compiler} ${cmake_cxx_flags}"
 
+#-----------------------------------------------------------------------------
 # Test Make
 
 cmake_make_processor=