Add declarations for ssyrk_ and dsyrk_ when cblas is not available

[d-torrance]

Otherwise, we get the following in config.log even when BLAS is available:

configure:18317: g++ -o conftest  -std=gnu++14 -g3 -O2  -w  -I. -I.. -I. -I./fflas-ffpack -I/M2/M2/BUILD/usr-host/include  -I/M2/M2/BUILD/../include -I/M2/M2\
/BUILD/include -I/M2/M2/BUILD/usr-host/include -isystem /usr/include/libxml2    -DNDEBUG -I/usr/include/eigen3  -I/usr/include/python3.6m -I/usr/include -DBO\
OST_STACKTRACE_LINK -L/M2/M2/BUILD/usr-host/lib -g3 -L/usr/lib64 conftest.cpp  -lrefblas -llapack >&5
In file included from conftest.cpp:68:
fflas-ffpack/config-blas.h: In function 'void cblas_ssyrk(CBLAS_ORDER, CBLAS_UPLO, CBLAS_TRANSPOSE, int, int, float, const float*, int, float, float*, int)':
fflas-ffpack/config-blas.h:296:12: error: 'ssyrk_' was not declared in this scope
            ssyrk_ (EXT_BLAS_UPLO_tr(Uplo), EXT_BLAS_TRANSPOSE(Trans), N, K, alpha, A, lda, beta, C, ldc); // @TODO check this
            ^~~~~~
fflas-ffpack/config-blas.h:296:12: note: suggested alternative: 'sscal_'
            ssyrk_ (EXT_BLAS_UPLO_tr(Uplo), EXT_BLAS_TRANSPOSE(Trans), N, K, alpha, A, lda, beta, C, ldc); // @TODO check this
            ^~~~~~
            sscal_
fflas-ffpack/config-blas.h:298:12: error: 'ssyrk_' was not declared in this scope
            ssyrk_ (EXT_BLAS_UPLO (Uplo), EXT_BLAS_TRANSPOSE(Trans), N, K, alpha, A, lda, beta, C, ldc);
            ^~~~~~
fflas-ffpack/config-blas.h:298:12: note: suggested alternative: 'sscal_'
            ssyrk_ (EXT_BLAS_UPLO (Uplo), EXT_BLAS_TRANSPOSE(Trans), N, K, alpha, A, lda, beta, C, ldc);
            ^~~~~~
            sscal_
fflas-ffpack/config-blas.h: In function 'void cblas_dsyrk(CBLAS_ORDER, CBLAS_UPLO, CBLAS_TRANSPOSE, int, int, double, const double*, int, double, double*, in\
t)':
fflas-ffpack/config-blas.h:305:13: error: 'dsyrk_' was not declared in this scope
             dsyrk_ (EXT_BLAS_UPLO_tr(Uplo), EXT_BLAS_TRANSPOSE(Trans), N, K, alpha, A, lda, beta, C, ldc); // @TODO check this
             ^~~~~~
fflas-ffpack/config-blas.h:305:13: note: suggested alternative: 'dscal_'
             dsyrk_ (EXT_BLAS_UPLO_tr(Uplo), EXT_BLAS_TRANSPOSE(Trans), N, K, alpha, A, lda, beta, C, ldc); // @TODO check this
             ^~~~~~
             dscal_
fflas-ffpack/config-blas.h:307:13: error: 'dsyrk_' was not declared in this scope
             dsyrk_ (EXT_BLAS_UPLO (Uplo), EXT_BLAS_TRANSPOSE(Trans), N, K, alpha, A, lda, beta, C, ldc);
             ^~~~~~
fflas-ffpack/config-blas.h:307:13: note: suggested alternative: 'dscal_'
             dsyrk_ (EXT_BLAS_UPLO (Uplo), EXT_BLAS_TRANSPOSE(Trans), N, K, alpha, A, lda, beta, C, ldc);
             ^~~~~~
             dscal_
configure:18317: $? = 1
configure: program exited with status 1

[d-torrance]

I added an additional commit -- cblas_dsyrk was missing static inline like the other wrappers, which was leading to "multiple definition" errors when linking.