gsl: Add workaround for Android 5 linker issue

Fixes #507.

packages/gsl/build.sh

@@ -1,5 +1,10 @@
 TERMUX_PKG_HOMEPAGE=http://www.gnu.org/software/gsl/
 TERMUX_PKG_DESCRIPTION="GNU Scientific Library (GSL) providing a wide range of mathematical routines"
 TERMUX_PKG_VERSION=2.2.1
+TERMUX_PKG_BUILD_REVISION=1
 TERMUX_PKG_SRCURL=https://mirrors.kernel.org/gnu/gsl/gsl-${TERMUX_PKG_VERSION}.tar.gz
 TERMUX_PKG_RM_AFTER_INSTALL="bin/ share/man/man1"
+
+# Workaround for linker on Android 5 (fixed in Android 6) not supporting RTLD_GLOBAL.
+# See https://github.com/termux/termux-packages/issues/507
+export GSL_LDFLAGS="-Lcblas/.libs/ -lgslcblas"