Define __TERMUX__ and __TERMUX_PREFIX__

By defining __TERMUX__ and __TERMUX_PREFIX__ in <sys/cdefs.h> (which is
basically always included) one can more easily target Termux
specifically, both when cross-compiling packages and when code is built
on-device.

ndk-patches/sys-cdefs.h.patch

@@ -14,3 +14,10 @@ diff -uNr sysroot.orig/usr/include/sys/cdefs.h sysroot/usr/include/sys/cdefs.h
  #  define __USE_FILE_OFFSET64 1
  /*
   * Note that __RENAME_IF_FILE_OFFSET64 is only valid if the off_t and off64_t
+@@ -336,3 +340,6 @@
+ 
+ #include <android/versioning.h>
+ #include <android/api-level.h>
++
++#define __TERMUX__ 1
++#define __TERMUX_PREFIX__ "@TERMUX_PREFIX@"

packages/ndk-sysroot/build.sh

@@ -2,7 +2,7 @@ TERMUX_PKG_HOMEPAGE=https://developer.android.com/tools/sdk/ndk/index.html
 TERMUX_PKG_DESCRIPTION="System header and library files from the Android NDK needed for compiling C programs"
 TERMUX_PKG_LICENSE="NCSA"
 TERMUX_PKG_VERSION=$TERMUX_NDK_VERSION
-TERMUX_PKG_REVISION=3
+TERMUX_PKG_REVISION=4
 TERMUX_PKG_SKIP_SRC_EXTRACT=true
 # This package has taken over <pty.h> from the previous libutil-dev
 # and iconv.h from libandroid-support-dev:

scripts/build/termux_step_start_build.sh

@@ -11,7 +11,7 @@ termux_step_start_build() {
 	TERMUX_STANDALONE_TOOLCHAIN="$TERMUX_COMMON_CACHEDIR/android-r${TERMUX_NDK_VERSION}-api-${TERMUX_PKG_API_LEVEL}"
 	# Bump the below version if a change is made in toolchain setup to ensure
 	# that everyone gets an updated toolchain:
-	TERMUX_STANDALONE_TOOLCHAIN+="-v1"
+	TERMUX_STANDALONE_TOOLCHAIN+="-v2"
 
 	if [ -n "${TERMUX_PKG_BLACKLISTED_ARCHES:=""}" ] && [ "$TERMUX_PKG_BLACKLISTED_ARCHES" != "${TERMUX_PKG_BLACKLISTED_ARCHES/$TERMUX_ARCH/}" ]; then
 		echo "Skipping building $TERMUX_PKG_NAME for arch $TERMUX_ARCH"