Build requires clblast, clblas is not sufficient

Building against clblas fails to link with

/usr/bin/ld: ./.libs/liboct.a(accel_blas.o): in function `__accel_blas_oct_m_MOD_daccel_gemv':
accel_blas_oct.f90:(.text+0x180): undefined reference to `clblasdgemvex_low_'
/usr/bin/ld: ./.libs/liboct.a(accel_blas.o): in function `__accel_blas_oct_m_MOD_zaccel_gemv':
accel_blas_oct.f90:(.text+0x125f): undefined reference to `clblaszgemvex_low_'
/usr/bin/ld: ./.libs/liboct.a(accel_blas.o): in function `__accel_blas_oct_m_MOD_zaccel_dotu':
accel_blas_oct.f90:(.text+0x1742): undefined reference to `clblaszdotu_low_'
collect2: error: ld returned 1 exit status

These functions are only defined in src/basic/clblast_low.c which has an #ifdef HAVE_CLBLAST around the entire body.