Introduce package to capture dependency on C++ stdlib

Here we introduce a new "virtual" package into the initial package
database, `system-cxx-std-lib`. This gives users a convenient, platform
agnostic way to link against C++ libraries, addressing #20010.

Fixes #20010.

1 files changed, 58 insertions, 0 deletions

diff --git a/m4/fp_find_cxx_std_lib.m4 b/m4/fp_find_cxx_std_lib.m4
new file mode 100644
index 0000000000..d0bb3195c6
--- /dev/null
+++ b/m4/fp_find_cxx_std_lib.m4
@@ -0,0 +1,58 @@
+# FP_FIND_CXX_STD_LIB
+# -------------------
+#
+# Identify which C++ standard library implementation the C++ toolchain links
+# against.
+AC_DEFUN([FP_FIND_CXX_STD_LIB],[
+    # If this is non-empty then assume that the user has specified these
+    # manually.
+    if test -z "$CXX_STD_LIB_LIBS"; then
+        cat >actest.cpp <<-EOF
+#include <iostream>
+#if defined(_LIBCPP_VERSION)
+libc++
+#elif defined(__GLIBCXX__)
+libstdc++
+#else
+unknown
+#endif
+EOF
+        AC_MSG_CHECKING([C++ standard library flavour])
+        if "$CXX" -E actest.cpp -o actest.out; then
+            if grep "libc++" actest.out; then
+                CXX_STD_LIB_LIBS="c++ c++abi"
+                p="`"$CXX" --print-file-name libc++.so`"
+                d="`dirname "$p"`"
+                dnl On some platforms (e.g. Windows) the C++ standard library
+                dnl can be found in the system search path. In this case $CXX
+                dnl --print-file-name will simply print the filename without a
+                dnl directory part. Consequently, dirname will return `.`. However,
+                dnl we don't want to include such paths in the package database.
+                if test "$d" = "."; then d=""; fi
+                CXX_STD_LIB_LIB_DIRS="$d"
+                CXX_STD_LIB_DYN_LIB_DIRS="$d"
+                AC_MSG_RESULT([libc++])
+            elif grep "libstdc++" actest.out; then
+                CXX_STD_LIB_LIBS="stdc++"
+                p="`"$CXX" --print-file-name libstdc++.so`"
+                d="`dirname "$p"`"
+                if test "$d" = "."; then d=""; fi
+                CXX_STD_LIB_LIB_DIRS="$d"
+                CXX_STD_LIB_DYN_LIB_DIRS="$d"
+                AC_MSG_RESULT([libstdc++])
+            else
+                rm -f actest.cpp actest.out
+                AC_MSG_ERROR([Unknown C++ standard library implementation.])
+            fi
+            rm -f actest.cpp actest.out
+        else
+            rm -f actest.cpp actest.out
+            AC_MSG_ERROR([Failed to compile test program])
+        fi
+    fi
+
+    AC_SUBST([CXX_STD_LIB_LIBS])
+    AC_SUBST([CXX_STD_LIB_LIB_DIRS])
+    AC_SUBST([CXX_STD_LIB_DYN_LIB_DIRS])
+])
+