Support shared libraries on Android (using make)

While the rest of the make build system maps Android to Linux, Android
uses unversioned shared libraries (like "libpq.so").  This patch makes
it so.  (Meson already supported it.)

Reported-by: Matthias Kuhn <matthias@opengis.ch>
Discussion: https://www.postgresql.org/message-id/flat/CAC7zN94TdsHhY88XkroJzSMx7E%3DBQpV9LKKjNSEnTM04ihoWCA%40mail.gmail.com

src/Makefile.shlib

@@ -183,6 +183,11 @@ endif
 ifeq ($(PORTNAME), linux)
   LINK.shared		= $(COMPILER) -shared
   ifdef soname
+    ifneq (,$(findstring linux-android,$(host_os)))
+      # Android uses unversioned shared libraries
+      shlib		= $(shlib_bare)
+      soname		= $(shlib_bare)
+    endif
     LINK.shared		+= -Wl,-soname,$(soname)
   endif
   BUILD.exports		= ( echo '{ global:'; $(AWK) '/^[^\#]/ {printf "%s;\n",$$1}' $<; echo ' local: *; };' ) >$@