Improve error messages by including symbol index in trampolines

We smuggle symbol indices in a scratch register through our
trampolines, allowing our default error printing function to rescue out
the appropriate symbol index, and turn that into a symbol name.
While this is fancy, reduces code size, and makes me feel clever, it's
also not very reproducible for other projects that wish to replicate
this technique without requiring that the scratch register be preserved
long enough for their handling code to get at it.  In such a case, the
fallback implementation would be to generate function stubs for every
symbol individually.  A Julia implementation of this follows:

First, a module is defined with error stubs for every symbol:
```julia
module LBTDebuggingFuncs
import LinearAlgebra.BLAS: lbt_get_config
for func_name in lbt_get_config().exported_symbols
    @eval $(Symbol(func_name))() = println("Error: no BLAS/LAPACK library loaded for ", $(func_name), "()!")
end
end # module LBTDebuggingFuncs
```

Next, these functions are inserted as the base layer of forwards for LBT:
```julia
symbol_list = lbt_get_config().exported_symbols
for (symbol_idx, symbol) in enumerate(symbol_list)
    func = getproperty(LBTDebuggingFuncs, Symbol(symbol))
    debug_fptr = @cfunction($func, Cvoid, ())
    lbt_set_forward_by_index(symbol_idx-1, debug_fptr, :ilp64)
    lbt_set_forward_by_index(symbol_idx-1, debug_fptr, :lp64)
end
```

After that, subsequent `lbt_forward()` calls (without `clear` set, of
course) will fill in forwards to the actual backing BLAS calls, but
those left behind will have customized error messages, denoting which
BLAS call was unsupported.

ext/gensymbol/generate_func_list.sh

@@ -37,7 +37,7 @@ echo "#ifndef EXPORTED_FUNCS" >> "${OUTPUT_FILE}"
 echo "#define EXPORTED_FUNCS(XX) \\" >> "${OUTPUT_FILE}"
 NUM_EXPORTED=0
 for s in ${EXPORTED_FUNCS}; do
-    echo "    XX(${s}) \\" >> "${OUTPUT_FILE}"
+    echo "    XX(${s}, ${NUM_EXPORTED}) \\" >> "${OUTPUT_FILE}"
     NUM_EXPORTED=$((${NUM_EXPORTED} + 1))
     [ $((${NUM_EXPORTED} % 100)) == 0 ] && echo -n "."
 done

src/Make.inc

@@ -53,7 +53,7 @@ else
   SONAME_FLAG := -Wl,-soname=$(LIB_MAJOR_VERSION)
 endif
 
-LBT_CFLAGS := -g -O2 -std=c99 $(FPIC) -DLIBRARY_EXPORTS -D_GNU_SOURCE $(CFLAGS)
+LBT_CFLAGS := -g -O2 -std=gnu99 $(FPIC) -DLIBRARY_EXPORTS -D_GNU_SOURCE -DARCH_$(ARCH) $(CFLAGS)
 LBT_LDFLAGS := $(LDFLAGS)
 
 ifeq ($(OS),Linux)