Avoid using the nonstandard "which" command

This command isn't a standard tool; different distributions have
different implementations, and e.g. Fedora doesn't ship it by
default.

Settle on using "command -v $tool >/dev/null" for tests about whether
a tool is available. (We could also use "hash $tool 2>/dev/null" as we
already had in build-all.sh, but settling on using "command -v"
everywhere, for consistency and simplicity.)

build-all.sh

@@ -60,7 +60,7 @@ if [ -z "$PREFIX" ]; then
 fi
 
 for dep in git curl cmake; do
-    if ! hash $dep 2>/dev/null; then
+    if ! command -v $dep >/dev/null; then
         echo "$dep not installed. Please install it and retry" 1>&2
         exit 1
     fi

build-compiler-rt.sh

@@ -47,7 +47,7 @@ if [ ! -d llvm-project/compiler-rt ] || [ -n "$SYNC" ]; then
     CHECKOUT_ONLY=1 ./build-llvm.sh
 fi
 
-if [ -n "$(which ninja)" ]; then
+if command -v ninja >/dev/null; then
     CMAKE_GENERATOR="Ninja"
     NINJA=1
     BUILDCMD=ninja

build-libcxx.sh

@@ -55,7 +55,7 @@ LLVM_PATH="$(pwd)/llvm"
 
 cd runtimes
 
-if [ -n "$(which ninja)" ]; then
+if command -v ninja >/dev/null; then
     CMAKE_GENERATOR="Ninja"
     NINJA=1
     BUILDCMD=ninja

build-libssp.sh

@@ -22,7 +22,7 @@ if [ $# -lt 1 ]; then
 fi
 
 MAKE=make
-if [ -n "$(which gmake)" ]; then
+if command -v gmake >/dev/null; then
     MAKE=gmake
 fi
 
@@ -37,7 +37,7 @@ export PATH="$PREFIX/bin:$PATH"
 : ${ARCHS:=${TOOLCHAIN_ARCHS-i686 x86_64 armv7 aarch64}}
 
 download() {
-    if [ -n "$(which wget)" ]; then
+    if command -v wget >/dev/null; then
         if [ -n "$2" ]; then
             wget -O "$2" "$1"
         else

build-lldb-mi.sh

@@ -51,7 +51,7 @@ if [ -n "$SYNC" ] || [ -n "$CHECKOUT" ]; then
     cd ..
 fi
 
-if [ -n "$(which ninja)" ]; then
+if command -v ninja >/dev/null; then
     CMAKE_GENERATOR="Ninja"
     NINJA=1
     BUILDCMD=ninja

build-llvm.sh

@@ -125,7 +125,7 @@ fi
 
 [ -z "$CHECKOUT_ONLY" ] || exit 0
 
-if [ -n "$(which ninja)" ]; then
+if command -v ninja >/dev/null; then
     CMAKE_GENERATOR="Ninja"
     NINJA=1
     BUILDCMD=ninja
@@ -165,8 +165,8 @@ if [ -n "$HOST" ]; then
             break
         fi
     done
-    if [ -z "$native" ] && [ -n "$(which llvm-tblgen)" ]; then
+    if [ -z "$native" ] && command -v llvm-tblgen >/dev/null; then
-        native="$(dirname $(which llvm-tblgen))"
+        native="$(dirname $(command -v llvm-tblgen))"
         suffix=""
         if [ -x "$native/llvm-tblgen.exe" ]; then
             suffix=".exe"
@@ -191,7 +191,7 @@ if [ -n "$HOST" ]; then
             CMAKEFLAGS="$CMAKEFLAGS -DCLANG_PSEUDO_GEN=$native/clang-pseudo-gen$suffix"
         fi
     fi
-    CROSS_ROOT=$(cd $(dirname $(which $HOST-gcc))/../$HOST && pwd)
+    CROSS_ROOT=$(cd $(dirname $(command -v $HOST-gcc))/../$HOST && pwd)
     CMAKEFLAGS="$CMAKEFLAGS -DCMAKE_FIND_ROOT_PATH=$CROSS_ROOT"
     CMAKEFLAGS="$CMAKEFLAGS -DCMAKE_FIND_ROOT_PATH_MODE_PROGRAM=NEVER"
     CMAKEFLAGS="$CMAKEFLAGS -DCMAKE_FIND_ROOT_PATH_MODE_INCLUDE=ONLY"

build-make.sh

@@ -45,7 +45,7 @@ PREFIX="$(cd "$PREFIX" && pwd)"
 : ${ARCHS:=${TOOLCHAIN_ARCHS-i686 x86_64 armv7 aarch64}}
 
 download() {
-    if [ -n "$(which wget)" ]; then
+    if command -v wget >/dev/null; then
         wget "$1"
     else
         curl -LO "$1"

build-mingw-w64-tools.sh

@@ -49,7 +49,7 @@ fi
 cd mingw-w64
 
 MAKE=make
-if [ -n "$(which gmake)" ]; then
+if command -v gmake >/dev/null; then
     MAKE=gmake
 fi
 

build-mingw-w64.sh

@@ -62,7 +62,7 @@ fi
 [ -z "$CHECKOUT_ONLY" ] || exit 0
 
 MAKE=make
-if [ -n "$(which gmake)" ]; then
+if command -v gmake >/dev/null; then
     MAKE=gmake
 fi
 

build-openmp.sh

@@ -35,7 +35,7 @@ fi
 
 cd llvm-project/openmp
 
-if [ -n "$(which ninja)" ]; then
+if command -v ninja >/dev/null; then
     CMAKE_GENERATOR="Ninja"
     NINJA=1
     BUILDCMD=ninja

build-python.sh

@@ -48,7 +48,7 @@ if [ -z "$CHECKOUT_ONLY" ]; then
 fi
 
 MAKE=make
-if [ -n "$(which gmake)" ]; then
+if command -v gmake >/dev/null; then
     MAKE=gmake
 fi