Add WOLFSSL_BARMETAL macro

[jackctj117]

Description

Adds --enable-baremetal configure option and WOLFSSL_BAREMETAL macro to simplify configuration for bare-metal embedded systems. This option encapsulates commonly-used defines for bare-metal environments into a single flag.

The WOLFSSL_BAREMETAL macro defines:

• SINGLE_THREADED - No threading support
• NO_DEV_RANDOM - No /dev/random access
• NO_FILESYSTEM - No file system access
• NO_WRITEV - No writev() system call
• NO_STDIO_FILESYSTEM - No stdio-based file operations
• WOLFSSL_NO_SOCK - No socket support
• WOLFSSL_NO_GETPID - No process ID support
• NO_ASN_TIME - Conditionally defined only when WOLFCRYPT_ONLY is also defined. For systems without RTC, this bypasses certificate date checking.

Important: Users must provide their own entropy source when using this configuration since NO_DEV_RANDOM is defined. Implement wc_GenerateSeed() with platform-specific hardware RNG.

Changes based on reviewer feedback:

• Removed WOLFCRYPT_ONLY from the macro - users should enable it separately via --enable-cryptonly if needed
• Made NO_ASN_TIME conditional on WOLFCRYPT_ONLY to avoid forcing certificate date checking to be disabled

Testing

Tested with autotools build system:

./autogen.sh
./configure --enable-baremetal
grep WOLFSSL_BAREMETAL wolfssl/options.h  # Verified macro is defined
# Verified NO_ASN_TIME is NOT defined with just --enable-baremetal
make clean && make

Tested with both flags:

./configure --enable-baremetal --enable-cryptonly
# Verified NO_ASN_TIME IS defined when WOLFCRYPT_ONLY is present
make clean && make

Tested with CMake build system:

mkdir build && cd build
cmake -DWOLFSSL_BAREMETAL=yes ..
make

Verified that WOLFSSL_BAREMETAL in settings.h correctly defines all component macros when enabled, and that NO_ASN_TIME is only defined when WOLFCRYPT_ONLY is also present.

Checklist

• added tests
• updated/added doxygen
• updated appropriate READMEs
• Updated manual and documentation

Review Focus Areas

1. Conditional NO_ASN_TIME logic: Verify the #ifdef WOLFCRYPT_ONLY wrapper around NO_ASN_TIME is the intended behavior
2. Placement in settings.h: Confirm the WOLFSSL_BAREMETAL block at line 345 doesn't conflict with later platform-specific blocks
3. Entropy requirements: Users will need to provide their own wc_GenerateSeed() implementation - consider if this needs additional documentation

[dgarske]

Very nice! Is it possible to setup a CI build to test this and add a bit of documentation like the PR description has?

[dgarske]

Jenkins retest this please

[dgarske]

Closing this PR and will re-open in a fork.