lapack: Force gcc toolchain

It need gfortran to build and if we have clang as system compiler it
does not work properly to compile it.

Fixes
aarch64-yoe-linux-gfortran: fatal error: cannot read spec file 'libgfortran.spec': No such file or directory
compilation terminated.

Signed-off-by: Khem Raj <raj.khem@gmail.com>

meta-oe/recipes-devtools/lapack/lapack_3.12.1.bb

@@ -101,3 +101,6 @@ do_install_ptest () {
     sed -i -e 's#${PYTHON}#/usr/bin/python3#g' `find ${D}${PTEST_PATH} -name CTestTestfile.cmake`
     sed -i -e 's#${WORKDIR}##g' `find ${D}${PTEST_PATH} -name CTestTestfile.cmake`
 }
+
+# It needs fortran compiler and we do not enable fortran with clang yet
+TOOLCHAIN = "gcc"