Use the simulator deployment-target flag for simulator builds

-mios-version-min names the device platform, so against the simulator SDK the
linker rejects every dylib it resolves there. Configuring for the simulator
still exits 0, but conftest links fail and iconv, sqlite3 and zlib features are
misdetected as absent; a build with a library on LDFLAGS before the first
compiler check fails outright instead.

The device/simulator split is already known from the host triple, so select the
flag from it.

Author: clementperon

Misc/NEWS.d/next/Build/2026-08-20-14-02-33.gh-issue-156115.KXr8wU.rst

@@ -0,0 +1,4 @@
+iOS simulator builds are now configured with
+``-mios-simulator-version-min`` instead of the device's
+``-mios-version-min``. The device flag made the linker reject libraries
+resolved from the simulator SDK, so library detection silently failed.

configure

@@ -1008,8 +1008,13 @@ AS_CASE([$host],
 dnl Add the compiler flag for the iOS minimum supported OS version.
 AS_CASE([$ac_sys_system],
   [iOS], [
-    AS_VAR_APPEND([CFLAGS], [" -mios-version-min=${IPHONEOS_DEPLOYMENT_TARGET}"])
-    AS_VAR_APPEND([LDFLAGS], [" -mios-version-min=${IPHONEOS_DEPLOYMENT_TARGET}"])
+    dnl -mios-version-min names the device platform; against the simulator SDK it
+    dnl makes the linker reject every dylib it resolves there.
+    AS_IF([test "x$_host_device" = "xsimulator"],
+      [_ios_version_min_flag=-mios-simulator-version-min],
+      [_ios_version_min_flag=-mios-version-min])
+    AS_VAR_APPEND([CFLAGS], [" ${_ios_version_min_flag}=${IPHONEOS_DEPLOYMENT_TARGET}"])
+    AS_VAR_APPEND([LDFLAGS], [" ${_ios_version_min_flag}=${IPHONEOS_DEPLOYMENT_TARGET}"])
   ],
 )