gh-124932: Distinguish build prefix from host prefix in cross builds (#124933)

In Emscripten and other cross builds, the build file system and the host file
system look different. For instance, we may want to install into
`cross-build/$TARGET/lib`, and then mount that as `/lib` in the host file
system. This change adds a distinction between:

* `prefix` -- the path in the build file system where we want to install the files
* `host_prefix` -- the path in the host file system where getpath.c will look for the files

And similarly for `exec_prefix` and `host_exec_prefix`. At present, this is only
used for Emscripten.

1 files changed, 25 insertions, 0 deletions

diff --git a/configure b/configure
index 13c7d8a..7a778b4 100755
--- a/configure
+++ b/configure
@@ -1003,6 +1003,8 @@ LIPO_INTEL64_FLAGS
 LIPO_32BIT_FLAGS
 ARCH_RUN_32BIT
 UNIVERSALSDK
+host_exec_prefix
+host_prefix
 MACHDEP
 PKG_CONFIG_LIBDIR
 PKG_CONFIG_PATH
@@ -4105,6 +4107,29 @@ fi
 { printf "%s\n" "$as_me:${as_lineno-$LINENO}: result: \"$MACHDEP\"" >&5
 printf "%s\n" "\"$MACHDEP\"" >&6; }
 
+
+if test -z "$host_prefix"; then
+  case $ac_sys_system in #(
+  Emscripten) :
+    host_prefix=/ ;; #(
+  *) :
+    host_prefix='${prefix}'
+   ;;
+esac
+fi
+
+
+if test -z "$host_exec_prefix"; then
+  case $ac_sys_system in #(
+  Emscripten) :
+    host_exec_prefix=$host_prefix ;; #(
+  *) :
+    host_exec_prefix='${exec_prefix}'
+   ;;
+esac
+fi
+
+
 # On cross-compile builds, configure will look for a host-specific compiler by
 # prepending the user-provided host triple to the required binary name.
 #