CI: use -j1 like a coward

Zig's build script has several race conditions preventing proper
concurrent builds from working. By using -j1 for now, finishing this
branch (concurrent zig builds) is untangled from the separate problem of
correcting concurrency issues with zig's own build script.

In other words, let's solve one problem at a time.

Author: andrewrk

ci/aarch64-linux-debug.sh

@@ -60,6 +60,7 @@ stage3-debug/bin/zig build -Dtarget=arm-linux-musleabihf
 # TODO: add -fqemu back to this line
 
 stage3-debug/bin/zig build test docs \
+  -j1 \
   -fwasmtime \
   -Dstatic-llvm \
   -Dtarget=native-native-musl \

ci/aarch64-linux-release.sh

@@ -60,6 +60,7 @@ stage3-release/bin/zig build -Dtarget=arm-linux-musleabihf
 # TODO: add -fqemu back to this line
 
 stage3-release/bin/zig build test docs \
+  -j1 \
   -fwasmtime \
   -Dstatic-llvm \
   -Dtarget=native-native-musl \

ci/aarch64-macos.sh

@@ -44,6 +44,7 @@ PATH="$HOME/local/bin:$PATH" cmake .. \
 $HOME/local/bin/ninja install
 
 stage3-release/bin/zig build test docs \
+  -j1 \
   --zig-lib-dir "$(pwd)/../lib" \
   -Denable-macos-sdk \
   -Dstatic-llvm \

ci/x86_64-linux-debug.sh

@@ -58,6 +58,7 @@ stage3-debug/bin/zig fmt --check .. \
 stage3-debug/bin/zig build -Dtarget=arm-linux-musleabihf
 
 stage3-debug/bin/zig build test docs \
+  -j1 \
   -fqemu \
   -fwasmtime \
   -Dstatic-llvm \

ci/x86_64-linux-release.sh

@@ -59,6 +59,7 @@ stage3-release/bin/zig fmt --check .. \
 stage3-release/bin/zig build -Dtarget=arm-linux-musleabihf
 
 stage3-release/bin/zig build test docs \
+  -j1 \
   -fqemu \
   -fwasmtime \
   -Dstatic-llvm \

ci/x86_64-macos-debug.sh

@@ -48,6 +48,7 @@ cmake .. \
 make $JOBS install
 
 stage3/bin/zig build test docs \
+  -j1 \
   --zig-lib-dir "$(pwd)/../lib" \
   -Denable-macos-sdk \
   -Dstatic-llvm \

ci/x86_64-macos-release.sh

@@ -48,6 +48,7 @@ cmake .. \
 make $JOBS install
 
 stage3/bin/zig build test docs \
+  -j1 \
   --zig-lib-dir "$(pwd)/../lib" \
   -Denable-macos-sdk \
   -Dstatic-llvm \