Set accurate minimum SDK version in dylibs

We should set accurate minimum SDK version in produced dylibs. Otherwise
the individual versions of object files are ignored and we end up with
a file that may have higher minimum SDK version than requested.

Since here we don't have access to *_MIN_SDK_VERSION variables set in
build-libssl.sh, retrieve the minimum SDK version from the object files.
This give accurate information. Parse "otool -l" output for that. It's
more or less simple, once you account for peculiarities.

create-openssl-framework.sh

@@ -39,6 +39,45 @@ function check_bitcode() {
 	fi
 }
 
+# Inspect Mach-O load commands to get minimum SDK version.
+#
+# Depending on the actual minimum SDK version it may look like this
+# (for modern SDKs):
+#
+#     Load command 1
+#            cmd LC_BUILD_VERSION
+#        cmdsize 24
+#       platform 8
+#            sdk 13.2                   <-- target SDK
+#          minos 12.0                   <-- minimum SDK
+#         ntools 0
+#
+# Or like this for older versions, with a platform-dependent tag:
+#
+#     Load command 1
+#           cmd LC_VERSION_MIN_WATCHOS
+#       cmdsize 16
+#       version 4.0                     <-- minimum SDK
+#           sdk 6.1                     <-- target SDK
+function get_min_sdk() {
+    local file=$1
+    set +o pipefail
+    otool -l "$file" | awk "
+        /^Load command/ {
+            last_command = \"\"
+        }
+        \$1 == \"cmd\" {
+            last_command = \$2
+        }
+        (last_command ~ /LC_BUILD_VERSION/ && \$1 == \"minos\") ||
+        (last_command ~ /^LC_VERSION_MIN_/ && \$1 == \"version\") {
+            print \$2
+            exit
+        }
+    "
+    set -o pipefail
+}
+
 if [ $FWTYPE == "dynamic" ]; then
     DEVELOPER=`xcode-select -print-path`
     FW_EXEC_NAME="${FWNAME}.framework/${FWNAME}"
@@ -62,20 +101,21 @@ if [ $FWTYPE == "dynamic" ]; then
         CROSS_SDK="${PLATFORM}${SDKVERSION}.sdk"
         SDK="${CROSS_TOP}/SDKs/${CROSS_SDK}"
 
+        MIN_SDK_VERSION=$(get_min_sdk "${TARGETDIR}/lib/libcrypto.a")
         if [[ $PLATFORM == AppleTVSimulator* ]]; then
-            MIN_SDK="-tvos_simulator_version_min 11.0"
+            MIN_SDK="-tvos_simulator_version_min $MIN_SDK_VERSION"
         elif [[ $PLATFORM == AppleTV* ]]; then
-            MIN_SDK="-tvos_version_min 11.0"
+            MIN_SDK="-tvos_version_min $MIN_SDK_VERSION"
         elif [[ $PLATFORM == MacOSX* ]]; then
-            MIN_SDK="-macosx_version_min 10.11"
+            MIN_SDK="-macosx_version_min $MIN_SDK_VERSION"
         elif [[ $PLATFORM == iPhoneSimulator* ]]; then
-            MIN_SDK="-ios_simulator_version_min 11.0"
+            MIN_SDK="-ios_simulator_version_min $MIN_SDK_VERSION"
         elif [[ $PLATFORM == WatchOS* ]]; then
-            MIN_SDK="-watchos_version_min 4.0"
+            MIN_SDK="-watchos_version_min $MIN_SDK_VERSION"
         elif [[ $PLATFORM == WatchSimulator* ]]; then
-            MIN_SDK="-watchos_simulator_version_min 4.0"
+            MIN_SDK="-watchos_simulator_version_min $MIN_SDK_VERSION"
         else
-            MIN_SDK="-ios_version_min 11.0"
+            MIN_SDK="-ios_version_min $MIN_SDK_VERSION"
         fi
 
         #cd $TARGETDIR