Unnecessarily verbose error message when main is undefined

If the main function has been renamed or is otherwise not present in a Lean executable, lake build gives an error message referencing the linker and C compiler. I would expect it to instead tell the user that they need a main function. Right now it looks almost like Lean has a bug or that there is a problem with the C compiler's setup.

Steps to reproduce (I am on Linux Mint):

lake new myproject
cd myproject

Now, rename main to something else in Main.lean. Then run:

lake build

This will give an error message like:

info: myproject: no previous manifest, creating one from scratch
info: toolchain not updated; already up-to-date
✖ [8/8] Building myproject:exe
trace: .> /home/niels/.elan/toolchains/leanprover--lean4---v4.27.0/bin/clang -o /home/niels/Documents/Scratch/myproject/.lake/build/bin/myproject /home/niels/Documents/Scratch/myproject/.lake/build/ir/Main.c.o.export /home/niels/Documents/Scratch/myproject/.lake/build/ir/Myproject/Basic.c.o.export /home/niels/Documents/Scratch/myproject/.lake/build/ir/Myproject.c.o.export -L /home/niels/.elan/toolchains/leanprover--lean4---v4.27.0/lib/lean --sysroot /home/niels/.elan/toolchains/leanprover--lean4---v4.27.0 -L /home/niels/.elan/toolchains/leanprover--lean4---v4.27.0/lib -L /home/niels/.elan/toolchains/leanprover--lean4---v4.27.0/lib/glibc -lc -lc_nonshared -Wl,--as-needed -l:ld.so -Wl,--no-as-needed -lpthread_nonshared -Wl,--as-needed -Wl,-Bstatic -lgmp -lunwind -luv -Wl,-Bdynamic -Wl,--no-as-needed -fuse-ld=lld -Wl,--start-group -lleancpp -lLean -Wl,--end-group -lStd -Wl,--start-group -lInit -lleanrt -Wl,--end-group -Wl,-Bstatic -lc++ -lc++abi -Wl,-Bdynamic -lLake -Wl,--as-needed -lgmp -luv -lpthread -ldl -lrt -Wl,--no-as-needed -lm -ldl -pthread
info: stderr:
ld.lld: error: undefined symbol: main
>>> referenced by start.S:104 (../sysdeps/x86_64/start.S:104)
>>>               /home/niels/.elan/toolchains/leanprover--lean4---v4.27.0/lib/Scrt1.o:(_start)
clang: error: linker command failed with exit code 1 (use -v to see invocation)
error: external command '/home/niels/.elan/toolchains/leanprover--lean4---v4.27.0/bin/clang' exited with code 1
Some required targets logged failures:
- myproject:exe
error: build failed

I would rather it gave a message like:

error: build failed. Did not find a `main` function in the executable "myproject"

Reproduce the issue with a new project by renaming main in Main.lean and running lake build. Start from the executable build failure and make the missing-entry-point case report that no main function was found in the executable instead of exposing the linker and C compiler error; verify the revised message with the reproduction steps.