Build: Add -mno-strict-align flag for RISC-V architecture

[Polaris-911]

Description

This PR updates the root Makefile to automatically detect RISC-V architectures (via uname -m) and append the -mno-strict-align flag to MOREFLAGS.

On many RISC-V implementations standard builds can suffer from significant performance degradation. Adding -mno-strict-align instructs the compiler to generate code that handles unaligned accesses via byte-wise instructions or other safe methods, thereby avoiding expensive traps and improving runtime performance.

Changes

• Detects riscv% in UNAME_M.
• Appends -mno-strict-align to MOREFLAGS.
• Exports MOREFLAGS to ensure the flag is correctly propagated to sub-makefiles (lib, programs, etc.).

Validation & Benchmarks

Tested on a RISC-V device (Sophon SG2044 / 64-core RISC-V).

Benchmark Environment:

• Hardware: Sophon SG2044
• OS: Linux (RISC-V 64-bit)
• Compiler: GCC 12.3.1

Results:
Comparison between the original build and the build with -mno-strict-align.

Metric	Original	With -mno-strict-align	Improvement rate
Compression Speed	64.0 MB/s	75.2 MB/s	+17.50%
Decompression Speed	102.9 MB/s	165.1 MB/s	+60.45%

(Note: Data collected using zstd -b benchmark)