[OpenMP] libomp: fix non-X86 non-AARCH64 builds

[AndreyChurbanov]

Summary

Macro KMP_PREFIX_UNDERSCORE defined only for x86, x86_64 and aarch64 architectures.
This patch defines the macro to no-op in case it was not defined previously.

[Michael_Pique]

Adding that “emergency definition” of KMP_PREFIX_UNDERSCORE there at line 1730 seems reasonable. Similar code appears at lines 71 and 133; the function’s overall lack of orthogonality between OS and Hardware could be addressed later. I perceive no enthusiasm for a redesign.

[rogfer01]

Hi Andrey, I can confirm this fixes the build for RISC-V.

[kaz7]

Hi, it works fine for, not merged yet, VE architecture. Thank you for emergency patch.

[hbae]

LGTM.

openmp/runtime/src/z_Linux_asm.S

#if KMP_ARCH_ARM || KMP_ARCH_MIPS
     .align 4
     .global __kmp_unnamed_critical_addr
 __kmp_unnamed_critical_addr:
     .4byte .gomp_critical_user_
     .size __kmp_unnamed_critical_addr,4
 #endif /* KMP_ARCH_ARM */
 
 #if KMP_ARCH_PPC64 || KMP_ARCH_AARCH64 || KMP_ARCH_MIPS64 || KMP_ARCH_RISCV64
+#ifndef KMP_PREFIX_UNDERSCORE
+# define KMP_PREFIX_UNDERSCORE(x) x
+#endif
     .data
     .comm .gomp_critical_user_,32,8
     .data
     .align 8
     .global KMP_PREFIX_UNDERSCORE(__kmp_unnamed_critical_addr)
 KMP_PREFIX_UNDERSCORE(__kmp_unnamed_critical_addr):
     .8byte .gomp_critical_user_
 #ifdef __ELF__