Enable source/line info on "release" builds

The windows build already includes /Zi /Zl as part of commit 920fd2f
(PR #7840). It looks like it was simply missed on Unix.

This change also makes the native debug information closer to what
CoreCLR does on all platforms. See
dotnet/coreclr#3445 for more information.

This is also needed for the end-to-end debuginfo generation as part of
source-build. See dotnet/source-build#267

When packaging .NET for Linux distributions, the package builders
generally use a different workflow for shipping symbols to users:

1. The package maintainer builds code with the debug flags (such as
   `-g`) to generate full native debug info and symbols.

2. Nothing is stripped from build by the package maintainer.

3. The build system (`rpmbuild`, `debuild`) removes the debug
   info (or debug symbols) from the code and creates separate
   `-debuginfo` or `-debug` packages that contain just the debug
   symbols.

4. These debug packages are then distributed along with the normal
   packages using the normal Linux distribution mechanisms. This lets
   users install the exact set of debug symbols matching their other
   package.

To support this workflow in dotnet/runtime, we need to add optional
support for not stripping debug symbols. I used it has follows:

    CFLAGS=-g CXXFLAGS=-g ./build.sh --keepnativesymbols true

After this build, the built binaries include all debug symbols.

I can then rely on the distro package build system to identify, strip,
package and ship the debug info/symbols separately.

See dotnet#3781 and
dotnet/source-build#267 for more details on
the background and motivation.

For some related fixes, see:

- dotnet/coreclr#3445
- dotnet/corefx#24979

When packaging .NET for Linux distributions, the package builders
generally use a different workflow for shipping symbols to users:

1. The package maintainer builds code with the debug flags (such as
   `-g`) to generate full native debug info and symbols.

2. Nothing is stripped from build by the package maintainer.

3. The build system (`rpmbuild`, `debuild`) removes the debug
   info (or debug symbols) from the code and creates separate
   `-debuginfo` or `-debug` packages that contain just the debug
   symbols.

4. These debug packages are then distributed along with the normal
   packages using the normal Linux distribution mechanisms. This lets
   users install the exact set of debug symbols matching their other
   package.

To support this workflow in dotnet/runtime, we need to add optional
support for not stripping debug symbols. I used it has follows:

    CFLAGS=-g CXXFLAGS=-g ./build.sh --keepnativesymbols true

After this build, the built binaries include all debug symbols.

I can then rely on the distro package build system to identify, strip,
package and ship the debug info/symbols separately.

See #3781 and
dotnet/source-build#267 for more details on
the background and motivation.

For some related fixes, see:

- dotnet/coreclr#3445
- dotnet/corefx#24979

)

The windows build already includes /Zi /Zl as part of commit 920fd2f
(PR dotnet/corefx#7840). It looks like it was simply missed on Unix.

This change also makes the native debug information closer to what
CoreCLR does on all platforms. See
dotnet/coreclr#3445 for more information.

This is also needed for the end-to-end debuginfo generation as part of
source-build. See dotnet/source-build#267

Commit migrated from dotnet/corefx@efe7652