Use shed_yield() instead of pthread_yield() on Linux

Per https://man7.org/linux/man-pages/man3/pthread_yield.3.html
	This call is nonstandard, but present on several other systems.
        Use the standardized sched_yield(2) instead.

Should fix #299.

3rdp/build/GNUmakefile

@@ -82,7 +82,7 @@ $(CRYPT_SRC): | $(3RDPSRCDIR)
 $(CRYPT_IDIR): | $(3RDPODIR)
 	$(QUIET)$(IFNOTEXIST) mkdir $(CRYPT_IDIR)
 
-$(CRYPTLIB_BUILD): $(3RDP_ROOT)/dist/cryptlib.zip $(3RDP_ROOT)/build/terminal-params.patch $(3RDP_ROOT)/build/cl-mingw32-static.patch $(3RDP_ROOT)/build/cl-ranlib.patch $(3RDP_ROOT)/build/cl-win32-noasm.patch $(3RDP_ROOT)/build/cl-zz-country.patch $(3RDP_ROOT)/build/cl-algorithms.patch $(3RDP_ROOT)/build/cl-allow-duplicate-ext.patch $(3RDP_ROOT)/build/cl-macosx-minver.patch $(3RDP_ROOT)/build/cl-endian.patch $(3RDP_ROOT)/build/cl-cryptodev.patch $(3RDP_ROOT)/build/cl-posix-me-gently.patch $(3RDP_ROOT)/build/cl-tpm-linux.patch $(3RDP_ROOT)/build/cl-PAM-noprompts.patch $(3RDP_ROOT)/build/cl-zlib.patch $(3RDP_ROOT)/build/Dynamic-linked-static-lib.patch $(3RDP_ROOT)/build/SSL-fix.patch $(3RDP_ROOT)/build/cl-bigger-maxattribute.patch $(3RDP_ROOT)/build/cl-vcxproj.patch $(3RDP_ROOT)/build/cl-mingw-vcver.patch $(3RDP_ROOT)/build/cl-win32-build-fix.patch $(3RDP_ROOT)/build/cl-gcc-non-const-time-val.patch $(3RDP_ROOT)/build/cl-no-odbc.patch $(3RDP_ROOT)/build/cl-noasm-defines.patch $(3RDP_ROOT)/build/cl-bn-noasm64-fix.patch $(3RDP_ROOT)/build/cl-no-RSA-suites.patch $(3RDP_ROOT)/build/cl-fix-ECC-RSA.patch $(3RDP_ROOT)/build/cl-prefer-ECC.patch $(3RDP_ROOT)/build/cl-prefer-ECC-harder.patch $(3RDP_ROOT)/build/cl-more-RSA-ECC-fixes.patch $(3RDP_ROOT)/build/cl-DH-key-init.patch $(3RDP_ROOT)/build/cl-clear-GCM-flag.patch $(3RDP_ROOT)/build/cl-use-ssh-ctr.patch $(3RDP_ROOT)/build/cl-ssh-list-ctr-modes.patch $(3RDP_ROOT)/build/cl-ssh-incCtr.patch $(3RDP_ROOT)/build/cl-ssl-suite-blocksizes.patch $(3RDP_ROOT)/build/cl-no-tpm.patch $(3RDP_ROOT)/build/cl-no-via-aes.patch $(3RDP_ROOT)/build/cl-fix-ssh-ecc-ephemeral.patch $(3RDP_ROOT)/build/cl-just-use-cc.patch $(3RDP_ROOT)/build/cl-learn-numbers.patch $(3RDP_ROOT)/build/cl-no-safe-stack.patch $(3RDP_ROOT)/build/cl-allow-pkcs12.patch $(3RDP_ROOT)/build/cl-uint64_t-redefine.patch $(3RDP_ROOT)/build/cl-random-openbsd.patch $(3RDP_ROOT)/build/cl-openbsd-threads.patch $(3RDP_ROOT)/build/cl-allow-none-auth.patch $(3RDP_ROOT)/build/cl-mingw-add-m32.patch $(3RDP_ROOT)/build/cl-poll-not-select.patch $(3RDP_ROOT)/build/cl-check-before-use.patch | $(CRYPT_SRC) $(CRYPT_IDIR)
+$(CRYPTLIB_BUILD): $(3RDP_ROOT)/dist/cryptlib.zip $(3RDP_ROOT)/build/terminal-params.patch $(3RDP_ROOT)/build/cl-mingw32-static.patch $(3RDP_ROOT)/build/cl-ranlib.patch $(3RDP_ROOT)/build/cl-win32-noasm.patch $(3RDP_ROOT)/build/cl-zz-country.patch $(3RDP_ROOT)/build/cl-algorithms.patch $(3RDP_ROOT)/build/cl-allow-duplicate-ext.patch $(3RDP_ROOT)/build/cl-macosx-minver.patch $(3RDP_ROOT)/build/cl-endian.patch $(3RDP_ROOT)/build/cl-cryptodev.patch $(3RDP_ROOT)/build/cl-posix-me-gently.patch $(3RDP_ROOT)/build/cl-tpm-linux.patch $(3RDP_ROOT)/build/cl-PAM-noprompts.patch $(3RDP_ROOT)/build/cl-zlib.patch $(3RDP_ROOT)/build/Dynamic-linked-static-lib.patch $(3RDP_ROOT)/build/SSL-fix.patch $(3RDP_ROOT)/build/cl-bigger-maxattribute.patch $(3RDP_ROOT)/build/cl-vcxproj.patch $(3RDP_ROOT)/build/cl-mingw-vcver.patch $(3RDP_ROOT)/build/cl-win32-build-fix.patch $(3RDP_ROOT)/build/cl-gcc-non-const-time-val.patch $(3RDP_ROOT)/build/cl-no-odbc.patch $(3RDP_ROOT)/build/cl-noasm-defines.patch $(3RDP_ROOT)/build/cl-bn-noasm64-fix.patch $(3RDP_ROOT)/build/cl-no-RSA-suites.patch $(3RDP_ROOT)/build/cl-fix-ECC-RSA.patch $(3RDP_ROOT)/build/cl-prefer-ECC.patch $(3RDP_ROOT)/build/cl-prefer-ECC-harder.patch $(3RDP_ROOT)/build/cl-more-RSA-ECC-fixes.patch $(3RDP_ROOT)/build/cl-DH-key-init.patch $(3RDP_ROOT)/build/cl-clear-GCM-flag.patch $(3RDP_ROOT)/build/cl-use-ssh-ctr.patch $(3RDP_ROOT)/build/cl-ssh-list-ctr-modes.patch $(3RDP_ROOT)/build/cl-ssh-incCtr.patch $(3RDP_ROOT)/build/cl-ssl-suite-blocksizes.patch $(3RDP_ROOT)/build/cl-no-tpm.patch $(3RDP_ROOT)/build/cl-no-via-aes.patch $(3RDP_ROOT)/build/cl-fix-ssh-ecc-ephemeral.patch $(3RDP_ROOT)/build/cl-just-use-cc.patch $(3RDP_ROOT)/build/cl-learn-numbers.patch $(3RDP_ROOT)/build/cl-no-safe-stack.patch $(3RDP_ROOT)/build/cl-allow-pkcs12.patch $(3RDP_ROOT)/build/cl-uint64_t-redefine.patch $(3RDP_ROOT)/build/cl-random-openbsd.patch $(3RDP_ROOT)/build/cl-openbsd-threads.patch $(3RDP_ROOT)/build/cl-allow-none-auth.patch $(3RDP_ROOT)/build/cl-mingw-add-m32.patch $(3RDP_ROOT)/build/cl-poll-not-select.patch $(3RDP_ROOT)/build/cl-check-before-use.patch $(3RDP_ROOT)/build/cl-linux-yield.patch | $(CRYPT_SRC) $(CRYPT_IDIR)
 	@echo Creating $@ ...
 	$(QUIET)-rm -rf $(CRYPT_SRC)/*
 	$(QUIET)unzip -oa $(3RDPDISTDIR)/cryptlib.zip -d $(CRYPT_SRC)
@@ -136,6 +136,7 @@ $(CRYPTLIB_BUILD): $(3RDP_ROOT)/dist/cryptlib.zip $(3RDP_ROOT)/build/terminal-pa
 	$(QUIET)patch -b -p0 -d $(CRYPT_SRC) < cl-mingw-add-m32.patch
 	$(QUIET)patch -b -p0 -d $(CRYPT_SRC) < cl-poll-not-select.patch
 	$(QUIET)patch -b -p0 -d $(CRYPT_SRC) < cl-check-before-use.patch
+	$(QUIET)patch -b -p0 -d $(CRYPT_SRC) < cl-linux-yield.patch
 ifeq ($(os),win32)
 	$(QUIET)cd $(CRYPT_SRC) && env - PATH="$(PATH)" CC="$(CC)" AR="$(AR)" RANLIB="$(RANLIB)" make directories
 	$(QUIET)cd $(CRYPT_SRC) && env - PATH="$(PATH)" CC="$(CC)" AR="$(AR)" RANLIB="$(RANLIB)" make toolscripts

3rdp/build/cl-linux-yield.patch

+--- old/thread.h	2021-10-19 12:34:08.766649958 -0700
++++ kernel/thread.h	2021-10-19 12:34:43.794072316 -0700
+@@ -3005,7 +3005,7 @@
+   #endif /* Slowaris 5.7 / 7.x or newer */
+ #elif defined( _AIX ) || defined( __Android__ ) || defined( __CYGWIN__ ) || \
+ 	  ( defined( __hpux ) && ( OSVERSION >= 11 ) ) || \
+-	  defined( __NetBSD__ ) || defined( __QNX__ ) || defined( __UCLIBC__ )
++	  defined( __NetBSD__ ) || defined( __QNX__ ) || defined( __UCLIBC__ ) || defined(__linux__)
+   #define THREAD_YIELD()		sched_yield()
+ #elif defined( __XMK__ )
+   /* The XMK underlying scheduling object is the process context, for which